SERIAL: OMAP: Remove the slave idle handling from the driver

UART IP slave idle handling now taken care by runtime pm backend(hwmod layer)
so remove the hackery from the driver.

As discussed on the list, in future if dma mode needs to be brought
back to this driver, UART sysc handling needs to be updated in
framework such a way that no-idle/force idle profile can be supported.
Given the broken dma mode for OMAP uarts, its very unlikely.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Tested-by: Vaibhav Bedia <vaibhav.bedia@ti.com>
Tested-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Rajendra nayak <rnayak@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>  # OMAP4/Panda
Signed-off-by: Paul Walmsley <paul@pwsan.com>