ARM: OMAP2+: Fix section warning for pcm049

WARNING: vmlinux.o(.text+0x2d4e4): Section mismatch in reference from the function pcm049_display_init() to the function .init.tex)
The function pcm049_display_init() references
the function __init omap_mux_init_signal().
This is often because pcm049_display_init lacks a __init
annotation or the annotation of omap_mux_init_signal is wrong.

Folding this into the pcm049 patch in testing-board.

Signed-off-by: Tony Lindgren <tony@atomide.com>