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/cpu/ti/am335x/Kconfig

@@ -8,3 +8,11 @@ config CPU_TI_AM335X
 	select BOOT_DEVICE_NOT_SPI_FLASH
 	bool
 	default n
+
+if CPU_TI_AM335X
+
+config MEMLAYOUT_LD_FILE
+	string
+	default "src/cpu/ti/am335x/memlayout.ld"
+
+endif

src/cpu/ti/am335x/Makefile.inc

@@ -49,8 +49,5 @@ $(obj)/MLO: $(obj)/coreboot.rom $(obj)/omap-header.bin
 
 omap-header-y	+= header.c
 
-bootblock-y += memlayout.ld
-romstage-y += memlayout.ld
-ramstage-y += memlayout.ld
-omap-header-y += memlayout.ld
+omap-header-srcs += $(CONFIG_MEMLAYOUT_LD_FILE)
 omap-header-y += header.ld