treewide: Add Kconfig variable MEMLAYOUT_LD_FILE

This change defines a Kconfig variable MEMLAYOUT_LD_FILE which allows
SoC/mainboard to provide a linker file for the platform. x86 already
provides a default memlayout.ld under src/arch/x86. With this new
Kconfig variable, it is possible for the SoC/mainboard code for x86 to
provide a custom linker file as well.

Makefile.inc is updated for all architectures to use this new Kconfig
variable instead of assuming memlayout.ld files under a certain
path. All non-x86 boards used memlayout.ld under mainboard
directory. However, a lot of these boards were simply including the
memlayout from SoC. So, this change also updates these mainboards and
SoCs to define the Kconfig as required.

BUG=b:155322763
TEST=Verified that abuild with --timeless option results in the same
coreboot.rom image for all boards.

Change-Id: I6a7f96643ed0519c93967ea2c3bcd881a5d6a4d6
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42292
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/mediatek/mt8173/Kconfig

@@ -13,6 +13,10 @@ config SOC_MEDIATEK_MT8173
 
 if SOC_MEDIATEK_MT8173
 
+config MEMLAYOUT_LD_FILE
+	string
+	default "src/soc/mediatek/mt8173/memlayout.ld"
+
 config VBOOT
 	select VBOOT_MUST_REQUEST_DISPLAY
 	select VBOOT_STARTS_IN_BOOTBLOCK

src/soc/mediatek/mt8183/Kconfig

@@ -11,6 +11,10 @@ config SOC_MEDIATEK_MT8183
 
 if SOC_MEDIATEK_MT8183
 
+config MEMLAYOUT_LD_FILE
+	string
+	default "src/soc/mediatek/mt8183/memlayout.ld"
+
 config VBOOT
 	select VBOOT_MUST_REQUEST_DISPLAY
 	select VBOOT_STARTS_IN_BOOTBLOCK