tty: serial: cpm_uart - fix init when SMC is relocated

SMC relocation can also be activated earlier by the bootloader,
so the driver's behaviour cannot rely on selected kernel config.

When the SMC is relocated, CPM_CR_INIT_TRX cannot be used.

But the only thing CPM_CR_INIT_TRX does is to clear the
rstate and tstate registers, so this can be done manually,
even when SMC is not relocated.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Fixes: 9ab92120 ("cpm_uart: fix non-console port startup bug")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>