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>

Kconfig

@@ -276,9 +276,25 @@ config PHYS_64BIT
 	  This can be used not only for 64bit SoCs, but also for
 	  large physical address extension on 32bit SoCs.
 
+config HAS_ROM
+	bool
+	select BINMAN
+	help
+	  Enables building of a u-boot.rom target. This collects U-Boot and
+	  any necessary binary blobs.
+
+config ROM_NEEDS_BLOBS
+	bool
+	depends on HAS_ROM
+	help
+	  Enable this if building the u-boot.rom target needs binary blobs, and
+	  so cannot be done normally. In this case, pass BUILD_ROM=1 to make
+	  to tell U-Boot to build the ROM.
+
 config BUILD_ROM
 	bool "Build U-Boot as BIOS replacement"
-	depends on X86
+	depends on HAS_ROM
+	default y if !ROM_NEEDS_BLOBS
 	help
 	  This option allows to build a ROM version of U-Boot.
 	  The build process generally requires several binary blobs