ARM: OMAP: Move plat/i2c.h into mach-omap1 folder

The current contents of plat/i2c.h are only relevant for OMAP1
platforms, as all the equivalent functions for OMAP2 has been
dropped in commit 65fa3e71 ("ARM: OMAP2+: Remove legacy i2c.c
platform init code"), and which has also moved the left-over code
from plat-omap into mach-omap1. The hwmod is a concept only
applicable for OMAP2 platforms, and the omap_i2c_reset() is
already declared in mach-omap2/i2c.h. So, move the current
plat/i2c.h header file into the mach-omap1 folder, and adjust
the header usage accordingly.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>