ram: k3-ddrss: Use the DDR controller BIST engine for ECC priming

The 1-bit inline ECC support in TI's DDRSS bridge requires
the configured memory regions to be preloaded with a pattern
before use. This is done by the k3-ddrss driver from the
R5 SPL in a 'for' loop. It takes around 10 seconds to fill
2GB of memory, for example. Memset can cut the time in half
and using DMA currently yields a similar result.

The BIST engine of DDR controller provides support for
initializing any memory region with a pattern. This
bypasses the DDRSS bridge, so the required inline ECC
data is not computed and populated in the memory. For
some values like zero, the computed ECC syndrome is also
zero and we can use these values to preload the memory
from the DDR controller, without the assistance of the
bridge.

The registers involved in the process are described in the
'DDR controller registers' topic in [1] AM62 and [2] J721E
reference manuals.

The patch replaces the 'for' loop memory fill function with
the BIST memory initialization procedure. This cuts the time
to preload the 2GB memory from 10 seconds down to 1 second.
The bist preload function uses the lpddr4 APIs in the k3-ddrss,
so this is compatible with devices with both 16-bit LPDDR4 and
32-bit LPDDR4 interfaces (e.g J721E).

[1] AM62x: https://www.ti.com/lit/pdf/spruiv7
[2] DRA829/TDA4VM: https://www.ti.com/lit/zip/spruil1

Signed-off-by: Georgi Vlaev <g-vlaev@ti.com>
Signed-off-by: Santhosh Kumar K <s-k6@ti.com>

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