drm: bridge/dw_hdmi: clean up phy configuration

The phy configuration is dependent on the SoC, and we look up values for
some of the registers in SoC specific data.  However, we had partially
programmed the phy before we had successfully looked up the clock rate.
Also, we were only checking that we had a valid configuration for the
currctrl register.

Move all these lookups to the start of this function instead, so we can
check that all lookups were successful before beginning to program the
phy.

Tested-by: Yakir Yang <ykk@rock-chips.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>