serial:bfin_uart: Put TX IRQ in individual platform resource.

Serial TX IRQ is not RX IRQ plus 1 in some blackfin chips.
Give individual platform resources to both TX and RX irqs.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>