clk: Add get/enable/disable/release for a bulk of clocks

This patch adds a "bulk" API to the clock API in order to get/enable/disable
/release a group of clocks associated with a device.

This bulk API will avoid adding a copy of the same code to manage
a group of clocks in drivers.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Simon Glass <sjg@chromium.org>