clk: Add Fixed MMIO clock driver

This patch adds a driver for Fixed MMIO clock.
The driver reads a clock frequency value from a single 32-bit memory
mapped register and registers it as a fixed rate clock.

It can be enabled with COMMON_CLK_FIXED_MMIO Kconfig option.

Signed-off-by: Jan Kotas <jank@cadence.com>
[sboyd@kernel.org: Make of_fixed_mmio_clk_setup() static, use clk_hw
based APIs]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index 8a9440a..d6cd32b 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -27,6 +27,7 @@
 obj-$(CONFIG_ARCH_CLPS711X)		+= clk-clps711x.o
 obj-$(CONFIG_COMMON_CLK_CS2000_CP)	+= clk-cs2000-cp.o
 obj-$(CONFIG_ARCH_EFM32)		+= clk-efm32gg.o
+obj-$(CONFIG_COMMON_CLK_FIXED_MMIO)	+= clk-fixed-mmio.o
 obj-$(CONFIG_COMMON_CLK_GEMINI)		+= clk-gemini.o
 obj-$(CONFIG_COMMON_CLK_ASPEED)		+= clk-aspeed.o
 obj-$(CONFIG_ARCH_HIGHBANK)		+= clk-highbank.o