clk: iproc: Add PWRCTRL support

Some iProc SoC clocks use a different way to control clock power, via
the PWRDWN bit in the PLL control register.  Since the PLL control
register is used to access the PWRDWN bit, there is no need for the
pwr_base when this is being used.  A new flag, IPROC_CLK_EMBED_PWRCTRL,
has been added to identify this usage.  We can use the AON interface to
write the values to enable/disable PWRDOWN.

Signed-off-by: Jon Mason <jonmason@broadcom.com>
[sboyd@codeaurora.org: Remove useless parentheses]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>