ACPICA doesn't include protections around address space checking, Linux
build tests always complain increased sparse warnings around ACPICA
internal acpi_os_map/unmap_memory() invocations.  This patch tries to fix
this issue permanently.

There are 2 choices left for us to solve this issue:
 1. Add __iomem address space awareness into ACPICA.
 2. Remove sparse checker of __iomem from ACPICA source code.

This patch chooses solution 2, because:
 1.  Most of the acpi_os_map/unmap_memory() invocations are used for ACPICA.
     table mappings, which in fact are not IO addresses.
 2.  The only IO addresses usage is for "system memory space" mapping code in:
      drivers/acpi/acpica/exregion.c
      drivers/acpi/acpica/evrgnini.c
      drivers/acpi/acpica/exregion.c
    The mapped address is accessed in the handler of "system memory space"
    - acpi_ex_system_memory_space_handler().  This function in fact can be
    changed to invoke acpi_os_read/write_memory() so that __iomem can
    always be type-casted in the OSL layer.

According to the above investigation, we drew the following conclusion:
It is not a good idea to introduce __iomem address space awareness into
ACPICA mostly in order to protect non-IO addresses.

We can simply remove __iomem for acpi_os_map/unmap_memory() to remove
__iomem checker for ACPICA code. Then we need to enforce external usages
to invoke other APIs that are aware of __iomem address space.
The external usages are:
 drivers/acpi/apei/einj.c
 drivers/acpi/acpi_extlog.c
 drivers/char/tpm/tpm_acpi.c
 drivers/acpi/nvs.c

This patch thus performs cleanups in this way:
 1. Add acpi_os_map/unmap_iomem() to be invoked by non-ACPICA code.
 2. Remove __iomem from acpi_os_map/unmap_memory().

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

To avoid build problems and breaking dependencies between ACPI header
files, <acpi/acpi.h> should not be included directly by code outside
of the ACPI core subsystem.  However, that is possible if
<linux/acpi_io.h> is included, because that file contains
a direct inclusion of <acpi/acpi.h>.

For this reason, remove the direct <acpi/acpi.h> inclusion from
<linux/acpi_io.h>, move that file from include/linux/ to include/acpi/
and make <linux/acpi.h> include it for CONFIG_ACPI set along with the
other ACPI header files.  Accordingly, Remove the inclusions of
<linux/acpi_io.h> from everywhere.

Of course, that causes the contents of the new <acpi/acpi_io.h> file
to be available for CONFIG_ACPI set only, so intel_opregion.o that
depends on it should also depend on CONFIG_ACPI (and it really should
not be compiled for CONFIG_ACPI unset anyway).

References: https://01.org/linuxgraphics/sites/default/files/documentation/acpi_igd_opregion_spec.pdf
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
[rjw: Subject and changelog]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>