purism/librem_skl: add/use VBT file

Add VBT file extracted from vendor (AMI) firmware,
use by default to ensure functional display after
resume from S3 when using libgfxinit.

Test: build/boot Librem 13v2/3/4,15v3/4 boards, verify
functional display after resume from S3 when using libgfxinit.

Change-Id: I6bc5dab60e3601d56dae4300efee255d7c58329d
Signed-off-by: Matt DeVillier <matt.devillier@puri.sm>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37068
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/purism/librem_skl/Kconfig

@@ -5,6 +5,7 @@ config BOARD_PURISM_BASEBOARD_LIBREM_SKL
 	select HAVE_ACPI_RESUME
 	select HAVE_ACPI_TABLES
 	select INTEL_LPSS_UART_FOR_CONSOLE
+	select INTEL_GMA_HAVE_VBT
 	select SOC_INTEL_COMMON_BLOCK_HDA_VERB
 	select SOC_INTEL_SKYLAKE
 	select SPD_READ_BY_WORD
@@ -55,6 +56,11 @@ config VGA_BIOS_ID
 	default "8086,1916" if BOARD_PURISM_LIBREM13_V2 || BOARD_PURISM_LIBREM15_V3
 	default "8086,5916" if BOARD_PURISM_LIBREM13_V4 || BOARD_PURISM_LIBREM15_V4
 
+# Override the default variant behavior, since same VBT
+# is used for all variants.
+config INTEL_GMA_VBT_FILE
+	default "src/mainboard/$(MAINBOARDDIR)/data.vbt"
+
 config DIMM_MAX
 	int
 	default 1