ARM: mach-shmobile: PLL does not have to run constantly for HDMI

The PLLC2 clock on AP4 systems does not need to run constantly to be
able to use HDMI. The HDMI hotplug interrupt works without the PLL
too, after which all the necessary clocks will be turned on by the
runtime PM.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>