MIPS: ath79: add SoC detection code for AR934X

Also add 'soc_is_ar934[124x]' helper functions and a Kconfig
symbol for the AR934X SoCs.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Luis R. Rodriguez <mcgrof@qca.qualcomm.com>
Cc: linux-mips@linux-mips.org
Cc: mcgrof@infradead.org
Patchwork: https://patchwork.linux-mips.org/patch/3506/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/ath79/Kconfig b/arch/mips/ath79/Kconfig
index bc6edad..7db8e89 100644
--- a/arch/mips/ath79/Kconfig
+++ b/arch/mips/ath79/Kconfig
@@ -69,6 +69,10 @@
 	select USB_ARCH_HAS_EHCI
 	def_bool n
 
+config SOC_AR934X
+	select USB_ARCH_HAS_EHCI
+	def_bool n
+
 config ATH79_DEV_GPIO_BUTTONS
 	def_bool n