ARM: OMAP: Fix i2c cmdline initcall for multiplatform

We only want this initcall to run when the kernel is
booted on omap SoCs. Fix the issue by initializing the
the initcall from separately for omap1 and omap2+.

This fixes the issue for omap2+ multiplatform configs
as we are using omap_subsys_initcall there.

Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>