ARM: dts: dra7xx-clocks: Fixup IPU1 mux clock parent source

The IPU1 functional clock is the output of a mux clock (represented
by ipu1_gfclk_mux previously) and the clock source for this has been
updated to be sourced from dpll_core_h22x2_ck in commit 39879c7d
("ARM: dts: dra7xx-clocks: Source IPU1 functional clock from CORE DPLL").
ipu1_gfclk_mux is an obsolete clock now with the clkctrl conversion,
and this clock source parenting is lost during the new clkctrl layout
conversion.

Remove this stale clock and fix up the clock source for this mux
clock using the latest equivalent clkctrl clock. This restores the
previous logic and ensures that the IPU1 continues to run at the
same frequency of IPU2 and independent of the ABE DPLL.

Fixes: b5f8ffbb

 ("ARM: dts: dra7: convert to use new clkctrl layout")
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>