i2c-omap: Use dynamic clocking also on OMAP1 CPUs

This patch will fix the i2c-omap "controller timed out" error on
OMAP1710 (most probably will apply to 1510 as well). Error happens
randomly if dyn_tick is activated (CONFIG_NO_IDLE_HZ=y) and reason was
that ARMXOR_CK clock domain was stopped during MPU idle.

Patch basically creates and uses virtual i2c_fck clock domain which
prevents that its parent ARMXOR_CK is not stopped during MPU idle
whenever i2c_fck is enabled. Patch also makes i2c-omap implementation
between 24xx and OMAP1 more consistent with the clock usage and fixes two
minor bugs.

Signed-off-by: Jarkko Nikula <jarkko.nikula@nokia.com>
Signed-off-by: Juha Yrjölä <juha.yrjola@nokia.com>