MIPS: allow use of generic board

This patch allows MIPS boards to make use of generic board, replacing
arch/mips/lib/board.c with common/board_{f,r}.c and struct bd_info with
the asm-generic version.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
diff --git a/arch/mips/lib/Makefile b/arch/mips/lib/Makefile
index 88ef1c5..e483e86 100644
--- a/arch/mips/lib/Makefile
+++ b/arch/mips/lib/Makefile
@@ -5,7 +5,9 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
+ifndef CONFIG_SYS_GENERIC_BOARD
 obj-y	+= board.o
+endif
 obj-y	+= io.o
 
 obj-$(CONFIG_CMD_BOOTM) += bootm.o