xtensa: allow to build big endian toolchain

Thanks Max for the overlay and hints.

target/config/Config.in.cpu

@@ -1299,6 +1299,15 @@ config ADK_TARGET_CPU_XTENSA_DE212
 	select ADK_TARGET_KERNEL_ZIMAGE
 	depends on ADK_TARGET_ARCH_XTENSA
 
+config ADK_TARGET_CPU_XTENSA_KC705_BE
+	bool "kc705_be"
+	depends on ADK_TARGET_BIG_ENDIAN
+	select ADK_TARGET_WITH_NPTL
+	select ADK_TARGET_WITH_MMU
+	select ADK_KERNEL_XTENSA_VARIANT_DC233C
+	select ADK_TARGET_KERNEL_ZIMAGE
+	depends on ADK_TARGET_ARCH_XTENSA
+
 config ADK_TARGET_CPU_XTENSA_FSF
 	bool "fsf"
 	depends on ADK_TARGET_BIG_ENDIAN
@@ -1620,6 +1629,7 @@ config ADK_TARGET_CPU_TYPE
 	default "dc233c" if ADK_TARGET_CPU_XTENSA_DC233C
 	default "dc232b" if ADK_TARGET_CPU_XTENSA_DC232B
 	default "de212" if ADK_TARGET_CPU_XTENSA_DE212
+	default "kc705_be" if ADK_TARGET_CPU_XTENSA_KC705_BE
 	default "fsf" if ADK_TARGET_CPU_XTENSA_FSF
 	default "crisv10" if ADK_TARGET_CPU_CRIS_CRISV10
 	default "crisv32" if ADK_TARGET_CPU_CRIS_CRISV32