mb/google/rex: Disable `ACPI PM timer`

This patch deselects `USE_PM_ACPI_TIMER` kconfig to ensure that
ACPI PM timer remains disabled.

The PM timer (by PMC IP) consumes more power and blocks S0ix so the
timer is emulated by ucode to save power and unblock S0ix.

TEST=Able to boot Google, Rex and ensure PMC MMIO register 0x18fc
BIT 1 is set.

Signed-off-by: Subrata Banik <subratabanik@google.com>
Change-Id: I2a23b417ff7fb6328323380a7df46b4b397fc8eb
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69685
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>

src/mainboard/google/rex/Kconfig

@@ -106,4 +106,7 @@ config TPM_TIS_ACPI_INTERRUPT
 	int
 	default 35  # GPE0_DW1_03 (GPP_E03)
 
+config USE_PM_ACPI_TIMER
+	default n
+
 endif # BOARD_GOOGLE_REX_COMMON