x86: Change how selection of ROMs works

Most x86 boards build a u-boot.rom which is programmed into SPI flash. But
this is not unique to x86. For example some rockchip boards can also boot
from SPI flash.

Also, at least on x86, binary blobs are sadly quite common. It is not
possible to build a functional image without them, and U-Boot needs to
know this at build time.

Introduce a new CONFIG_HAS_ROM option which selects whether u-boot.rom is
built and a new CONFIG_ROM_NEEDS_BLOBS option to indicate whether binary
blobs are also needed. If they are not needed, it is safe to build the ROM
always. Otherwise we still require the BUILD_ROM environment variable.

For now this affects only x86, but future patches will enable this for
rockchip too.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/Kconfig

@@ -160,6 +160,7 @@ config X86
 	select TIMER
 	select USE_PRIVATE_LIBGCC
 	select X86_TSC_TIMER
+	imply HAS_ROM if X86_RESET_VECTOR
 	imply BLK
 	imply CMD_DM
 	imply CMD_FPGA_LOADMK

arch/x86/Kconfig

@@ -360,6 +360,8 @@ config HAVE_FSP
 	bool "Add an Firmware Support Package binary"
 	depends on !EFI
 	select USE_HOB
+	select HAS_ROM
+	select ROM_NEEDS_BLOBS
 	help
 	  Select this option to add an Firmware Support Package binary to
 	  the resulting U-Boot image. It is a binary blob which U-Boot uses
@@ -519,6 +521,8 @@ config ENABLE_MRC_CACHE
 
 config HAVE_MRC
 	bool "Add a System Agent binary"
+	select HAS_ROM
+	select ROM_NEEDS_BLOBS
 	depends on !HAVE_FSP
 	help
 	  Select this option to add a System Agent binary to

arch/x86/cpu/quark/Kconfig

@@ -24,6 +24,7 @@ if INTEL_QUARK
 
 config HAVE_RMU
 	bool "Add a Remote Management Unit (RMU) binary"
+	select ROM_NEEDS_BLOBS
 	help
 	  Select this option to add a Remote Management Unit (RMU) binary
 	  to the resulting U-Boot image. It is a data block (up to 64K) of