serial: omap: optimization with section annotations

Two functions:
omap_serial_fill_features_erratas() and
of_get_uart_port_info() are only called from probe().
Marking them as __devinit gives us another
oportunity to free some code after .init.text
is done.

Tested-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Ruchika Kharwar <ruchika@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>