mips: add base support for QCA/Atheros ath79 SOCs

This patch add some common code for QCA/Atheros ath79 SOCs such as
DDR tuning, chip reset and CPU detection.

Signed-off-by: Wills Wang <wills.wang@live.com>
diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index aec5a15..7a82316 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -8,6 +8,7 @@
 libs-y += arch/mips/lib/
 
 machine-$(CONFIG_SOC_AU1X00) += au1x00
+machine-$(CONFIG_ARCH_ATH79) += ath79
 machine-$(CONFIG_MACH_PIC32) += pic32
 
 machdirs := $(patsubst %,arch/mips/mach-%/,$(machine-y))