ARM: mach-shmobile: improve MIPI DSI clock configuration

Now, that the MIPI DSI driver implements runtime PM, we don't need anymore to
configure clocks statically in the platform code. This patch also adds a DSITX1
clock definition for sh7372 and attaches PHY clocks to respective devices.

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