serial: sccnxp: Implement polling mode

This patch adds support for polling work mode, i.e. system is perform
periodical check chip status when IRQ-line is not connected to CPU.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/platform_data/sccnxp.h

@@ -84,6 +84,8 @@ struct sccnxp_pdata {
 	const u8		reg_shift;
 	/* Modem control lines configuration */
 	const u32		mctrl_cfg[SCCNXP_MAX_UARTS];
+	/* Timer value for polling mode (usecs) */
+	const unsigned int	poll_time_us;
 	/* Called during startup */
 	void (*init)(void);
 	/* Called before finish */