ARM: socfpga: Add support to gate peripheral clocks

Add support to gate the clocks that directly feed peripherals. For clocks
with multiple parents, add the ability to determine the correct parent,
and also set parents. Also add support to calculate and set the clocks'
rate.

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Reviewed-by: Pavel Machek <pavel@denx.de>
Acked-by: Mike Turquette <mturquette@linaro.org>
Cc: Mike Turquette <mturquette@linaro.org>
CC: Arnd Bergmann <arnd@arndb.de>
CC: Olof Johansson <olof@lixom.net>
Cc: Pavel Machek <pavel@denx.de>
CC: <linux@arm.linux.org.uk>

v4:
- Add Acked-by: Mike Turquette

v3:
- Addressed comments from Pavel

v2:
- Fix space/indent errors
- Add streq for strcmp == 0
Signed-off-by: Olof Johansson <olof@lixom.net>