ARM: davinci: da8xx dt: make file local symbols static

Make some file-local functions static. This fixes the sparse
warnings:

  CHECK   arch/arm/mach-davinci/da8xx-dt.c
arch/arm/mach-davinci/da8xx-dt.c:23:13: warning: symbol 'da8xx_uart_clk_enable' was not declared. Should it be static?
arch/arm/mach-davinci/da8xx-dt.c:40:23: warning: symbol 'da850_auxdata_lookup' was not declared. Should it be static?

Signed-off-by: Sekhar Nori <nsekhar@ti.com>