mb/google/skyrim: Switch from LZMA to LZ4 compression for ramstage

Because skyrim is loading ramstage from SPI with the DMA engine, the
size of the compressed image is less important to load speed than
decompression time.

Because the LZ4 decompression is so much faster than LZMA, compressing
with LZ4 saves us roughly 30ms in boot time.

For size, we're spending roughly 57KiB:
fallback/ramstage 0x9b00 stage 130864 LZMA (305316 decompressed)
fallback/ramstage 0x9b00 stage 189126 LZ4  (305316 decompressed)

Right now we have 2MiB empty space in Skyrim's RO before this change,
and roughly 550KiB empty space in RW, so there aren't currently any
size worries.

Just for fun, I also tested uncompressed ramstage, and it was still
18ms faster than LZMA, but that makes it roughly 12ms slower than LZ4.

BUG=b:264409477
TEST=Boot skyrim, look at boot speed.

Signed-off-by: Martin Roth <martin.roth@amd.corp-partner.google.com>
Change-Id: Iedde6fc2db9d702c0ff2b0081e7baa254ac6699f
Reviewed-on: https://review.coreboot.org/c/coreboot/+/71675
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/mainboard/google/skyrim/Kconfig

@@ -37,6 +37,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select I2C_TPM
 	select MAINBOARD_HAS_CHROMEOS
 	select MAINBOARD_HAS_TPM2
+	select MB_COMPRESS_RAMSTAGE_LZ4
 	select SOC_AMD_MENDOCINO
 	select SOC_AMD_COMMON_BLOCK_I2C3_TPM_SHARED_WITH_PSP
 	select SOC_AMD_COMMON_BLOCK_USE_ESPI