mb/google/rex: Enable asynchronous End-Of-Post

Set the `SOC_INTEL_CSE_SEND_EOP_ASYNC' flag to request End-Of-Post
right after PCI enumeration and handle the command response at
`BS_PAYLOAD_BOOT'.

With these settings we have observed a boot time reduction of about
100ms on google/rex.

TEST=Tests on google/rex with `SOC_INTEL_CSE_SEND_EOP_ASYNC' show
End-Of-Post after PCI initialization and EOP message received at
`BS_PAYLOAD_BOOT'.

Change-Id: I27b540eeddcada521eba91fcc51504831d6dc855
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74562
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>

src/mainboard/google/rex/Kconfig

@@ -27,6 +27,7 @@ config BOARD_GOOGLE_REX_COMMON
 	select PMC_IPC_ACPI_INTERFACE
 	select SOC_INTEL_CSE_LITE_SKU
 	select SOC_INTEL_CSE_PRE_CPU_RESET_TELEMETRY_V2
+	select SOC_INTEL_CSE_SEND_EOP_ASYNC
 
 config BOARD_GOOGLE_BASEBOARD_REX
 	def_bool n

src/soc/intel/meteorlake/Kconfig

@@ -89,7 +89,7 @@ config CPU_SPECIFIC_OPTIONS
 	select SOC_INTEL_COMMON_PCH_CLIENT
 	select SOC_INTEL_COMMON_RESET
 	select SOC_INTEL_COMMON_BLOCK_IOC
-	select SOC_INTEL_CSE_SEND_EOP_LATE
+	select SOC_INTEL_CSE_SEND_EOP_LATE if !MAINBOARD_HAS_CHROMEOS
 	select SOC_INTEL_CSE_SET_EOP
 	select SOC_INTEL_GFX_NON_PREFETCHABLE_MMIO
 	select SOC_INTEL_MEM_MAPPED_PM_CONFIGURATION