build/boot/roms: support "all" if argument passed

e.g. -k ukqwerty

previously, this would not work:
./build boot roms -k ukqwerty all

only this would work:
./build boot roms all

this patch fixes the bug.

Signed-off-by: Leah Rowe <leah@libreboot.org>

script/build/boot/roms

@@ -37,6 +37,8 @@ main()
 		-k)
 			opts="${opts} -k ${2}"
 			shift ;;
+		all)
+			firstoption="all" ;;
 		*)
 			boards="${boards} ${1} " ;;
 		esac