mb/google/guybrush/bootblock: add comment on selecting eSPI interface

Setting the PM_ESPI_CS_USE_DATA2 bit in PM_SPI_PAD_PU_PD results in the
eSPI transactions being sent via the SPI2 pins instead of the SPI1 pins.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Iad8e3a48496a52c14c936ab77c75dc1b403f47bb
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58876
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/mainboard/google/guybrush/bootblock.c

@@ -63,6 +63,7 @@ void bootblock_mainboard_early_init(void)
 
 	/* Early eSPI interface configuration */
 
+	/* Use SPI2 pins for eSPI */
 	dword = pm_read32(PM_SPI_PAD_PU_PD);
 	dword |= PM_ESPI_CS_USE_DATA2;
 	pm_write32(PM_SPI_PAD_PU_PD, dword);