The CREG block on lpc18xx contains configuration register
for two low power clocks. Support enabling of these two
clocks with a clk driver that access CREG trough the
syscon regmap interface.

These clocks are needed to support peripherals like the
internal RTC on lpc18xx.
Signed-off-by: NJoachim Eastwood <manabian@gmail.com>
Signed-off-by: NStephen Boyd <sboyd@codeaurora.org>