x86/sev: Initialize RMPOPT configuration MSRs

The new RMPOPT instruction helps manage per-CPU RMP optimization
structures inside the CPU. It takes a 1GB-aligned physical address and
either returns the status of the optimizations or tries to enable the
optimizations.

Initialize the per-CPU RMPOPT table base to the starting physical
address.  This enables RMP optimization for up to 2 TB of system RAM on
all CPUs because this is the maximum the RMPOPT tables support.

The RMPOPT_BASE MSR can only be written after SNP is enabled, so the
enabling runs from the ccp SNP init path (and again on guest teardown)
rather than from an initcall. This is also in line with the intention to
not enable SNP by default but enable it on demand, when the ccp module
is loaded.

RMPOPT_BASE is programmed on all primary threads.  RMPOPT_EN cannot be
cleared while SNP is enabled, and CPU hotplug is disabled while SNP is
active, so once programmed the MSRs stay set on all CPUs until SNP is
disabled.  A set RMPOPT_EN on the local CPU therefore means the
programming has already been done and thus it can be skipped.

  [ bp:
    - Massage commit message
    - move enabling logic into the commit message
    - zap unnecessary comments
    - cleanup ]

Suggested-by: Thomas Lendacky <thomas.lendacky@amd.com>
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://patch.msgid.link/7fdf0f5b1be4b561c884c5200d6606a947cbc09d.1789594774.git.ashish.kalra@amd.com

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