MIPS: loongson: Add built-in DTB support

Since the current bootloader for Loongson-1 does not support FDT,
introduce CONFIG_BUILTIN_DTB_NAME to enable a built-in DTB.

Signed-off-by: Keguang Zhang <keguang.zhang@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Author: kelvincheung

arch/mips/boot/dts/loongson/Makefile

@@ -1,4 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0
+
+ifneq ($(CONFIG_BUILTIN_DTB_NAME),)
+dtb-y	:= $(addsuffix .dtb, $(CONFIG_BUILTIN_DTB_NAME))
+else
 dtb-$(CONFIG_MACH_LOONGSON64)	+= loongson64_2core_2k1000.dtb
 dtb-$(CONFIG_MACH_LOONGSON64)	+= loongson64c_4core_ls7a.dtb
 dtb-$(CONFIG_MACH_LOONGSON64)	+= loongson64c_4core_rs780e.dtb
@@ -10,3 +14,4 @@ dtb-$(CONFIG_MACH_LOONGSON32)	+= cq-t300b.dtb
 dtb-$(CONFIG_MACH_LOONGSON32)	+= ls1b-demo.dtb
 dtb-$(CONFIG_MACH_LOONGSON32)	+= lsgz_1b_dev.dtb
 dtb-$(CONFIG_MACH_LOONGSON32)	+= smartloong-1c.dtb
+endif

arch/mips/loongson32/Kconfig

@@ -36,3 +36,11 @@ config LOONGSON1_LS1C
 endchoice
 
 endif # MACH_LOONGSON32
+
+config BUILTIN_DTB_NAME
+	string "Source file for built-in DTB"
+	depends on BUILTIN_DTB
+	help
+	  Base name (without suffix, relative to arch/mips/boot/dts/loongson)
+	  for the DTS file that will be used to produce the DTB linked into
+	  the kernel.