mips: add initial support for qca956x referenced board

QCA9563 is CPU used on AP152 board :

    Clock speed : 750 MHz ,
    Arch :  Mips 74Kc,
    Eth : SGMII interface,
    MIMO config : 3 * 3 450M,
    2 * USB 2.0,

Signed-off-by: Rosy Song <rosysong@rosinson.com>

Changes for v2:
   - coding style cleanup
   - remove ununsed flash chip in defconfig
   - enable automatic icache / dcache size in defconfig

Changes for v3:
   - add detailed information for qca956x in commit message

Changes for v4:
   - remove pre-configured network settings in ap152.h

Changes for v5:
   - coding style cleanup
diff --git a/board/qca/ap152/MAINTAINERS b/board/qca/ap152/MAINTAINERS
new file mode 100644
index 0000000..785ec27
--- /dev/null
+++ b/board/qca/ap152/MAINTAINERS
@@ -0,0 +1,6 @@
+AP152 BOARD
+M:	Rosy Song <rosysong@rosinson.com>
+S:	Maintained
+F:	board/qca/ap152/
+F:	include/configs/ap152.h
+F:	configs/ap152_defconfig