serial: add UART_CAP_EFR and UART_CAP_SLEEP flags to 16C950 UARTs definition

Adding UART_CAP_EFR and UART_CAP_SLEEP flags will enable sleep mode
and automatic CTS flow control for 16C950 UARTs. It will also avoid
capabilities detection warning like this:

"ttyS0: detected caps 00000700 should be 00000100"

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>