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/arch/mips/mach-ath79/Makefile b/arch/mips/mach-ath79/Makefile
index 7aa40c6..fbd40c0 100644
--- a/arch/mips/mach-ath79/Makefile
+++ b/arch/mips/mach-ath79/Makefile
@@ -7,3 +7,4 @@
 obj-$(CONFIG_SOC_AR933X)	+= ar933x/
 obj-$(CONFIG_SOC_AR934X)	+= ar934x/
 obj-$(CONFIG_SOC_QCA953X)	+= qca953x/
+obj-$(CONFIG_SOC_QCA956X)	+= qca956x/