x86: Make ROM_SIZE configurable in Kconfig

Currently the ROM_SIZE is hardcoded to 8MB in arch/x86/Kconfig. This
will not be the case when adding additional board support. Hence we
make ROM_SIZE configurable (512KB/1MB/2MB/4MB/8MB/16MB) and have the
board Kconfig file select the default ROM_SIZE.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/board/google/chromebook_link/Kconfig b/board/google/chromebook_link/Kconfig
index 3a4f557..7f79fd2 100644
--- a/board/google/chromebook_link/Kconfig
+++ b/board/google/chromebook_link/Kconfig
@@ -19,6 +19,7 @@
 	select SOUTHBRIDGE_INTEL_C216
 	select HAVE_ACPI_RESUME
 	select MARK_GRAPHICS_MEM_WRCOMB
+	select BOARD_ROMSIZE_KB_8192
 
 config MMCONF_BASE_ADDRESS
 	hex