I2C: OMAP: make omap_i2c_unidle/idle functions depend on CONFIG_PM_RUNTIME

The functions omap_i2c_unidle/idle are called from omap_i2c_runtime_resume
and omap_i2c_runtime_suspend which is compiled for CONFIG_PM_RUNTIME.
This patch removes the omap_i2c_unidle/idle functions and folds them
into the runtime callbacks.

This fixes the below warn when CONFIG_PM_RUNTIME is not defined

 CC      arch/arm/mach-omap2/board-ti8168evm.o
drivers/i2c/busses/i2c-omap.c:272: warning: 'omap_i2c_unidle' defined but not used
drivers/i2c/busses/i2c-omap.c:293: warning: 'omap_i2c_idle' defined but not used
  CC      net/ipv4/ip_forward.o

Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>