Define RAMTOP for x86 only

This Kconfig is deprecated, new platforms need to locate
ramstage stack in CBMEM instead.

Change-Id: I20ece297302321337cc2ce17fdef0c55242a4fc3
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/15189
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/arch/x86/Kconfig

@@ -83,6 +83,11 @@ config RAMBASE
 	hex
 	default 0x100000
 
+config RAMTOP
+	hex
+	default 0x200000
+	depends on ARCH_X86
+
 # Traditionally BIOS region on SPI flash boot media was memory mapped right below
 # 4G and it was the last region in the IFD. This way translation between CPU
 # address space to flash address was trivial. However some IFDs on newer SoCs