omap24xx_check_revision, omap3_check_features,
omap3_check_revision, omap4_check_revision, omap3_cpuinfo
are not used elsewhere, it should be static

Also fixes the following sparse warnings:
arch/arm/mach-omap2/id.c:105:13: warning: symbol 'omap24xx_check_revision'
was not declared. Should it be static?
arch/arm/mach-omap2/id.c:167:13: warning: symbol 'omap3_check_features'
was not declared. Should it be static?
arch/arm/mach-omap2/id.c:189:13: warning: symbol 'omap3_check_revision'
was not declared. Should it be static?
arch/arm/mach-omap2/id.c:270:13: warning: symbol 'omap4_check_revision'
was not declared. Should it be static?
arch/arm/mach-omap2/id.c:300:13: warning: symbol 'omap3_cpuinfo'
was not declared. Should it be static?
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>