[M] Change in coreboot[master]: mb/google/rex: Implement S0ix hooks aka `MS0X` method

[Subrata Banik (Code Review)]

Attention is currently required from: Kapil Porwal, Ivy Jian, Sridhar Siricilla, Eric Lai, Utkarsh H Patel.

Hello build bot (Jenkins), Tarun Tuli, Kapil Porwal, Ivy Jian, Utkarsh H Patel, Eric Lai,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/70196

to look at the new patch set (#5).

Change subject: mb/google/rex: Implement S0ix hooks aka `MS0X` method
......................................................................

mb/google/rex: Implement S0ix hooks aka `MS0X` method

This patch ensures to be able to drive SYS_SLP_S0IX_L `low` based
on the state of the system while `SKL_S0_L` signal is `low` (while
the system is in S0ix).

Implemented runtime ASL method (MS0X) being called by PEPD device
_DSM to configure `SLP_S0_GATE (GPP_H14)` PIN at S0ix entry/exit.

Scope (_SB)
{
   Method (MS0X, 1, Serialized)
   {
      If ((Arg0 == One))
      {
         _SB.PCI0.CTXS (0x75)
      }
      Else
      {
         _SB.PCI0.STXS (0x75)
      }
}

BUG=b:256807255
TEST=Able to see SYS_SLP_S0IX_L goes low in S0ix.

Signed-off-by: Subrata Banik 
Change-Id: Ie6b5e066f228ea5dc79ae14dd803fc283fd248ce
---
M src/mainboard/google/rex/Kconfig
M src/mainboard/google/rex/mainboard.c
M src/mainboard/google/rex/variants/baseboard/include/baseboard/variants.h
M src/mainboard/google/rex/variants/baseboard/rex/include/baseboard/gpio.h
4 files changed, 84 insertions(+), 1 deletion(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/96/70196/5