cpm_uart: fix non-console port startup bug

After UART interrupt handler is installed and rx is enabled, if an rx
interrupt comes before hardware init, rx->cur will be updated. Then the
hardware init will reset BD and make rx->cur out of sync, move the hardware
init code before request_irq.

Signed-off-by: Xiaotian Feng <xiaotian.feng@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>