MIPS: ath25: Add basic AR2315 SoC support

Add basic support for Atheros AR2315+ SoCs: registers definition file
and initial setup code.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Cc: Linux MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/8239/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/ath25/Kconfig

@@ -2,3 +2,8 @@ config SOC_AR5312
 	bool "Atheros AR5312/AR2312+ SoC support"
 	depends on ATH25
 	default y
+
+config SOC_AR2315
+	bool "Atheros AR2315+ SoC support"
+	depends on ATH25
+	default y