spi: pxa2xx: Make LPSS SPI general register optional

General register located in LPSS SPI private register space is not found in
upcoming Intel LPSS platforms. Access it conditionally depending is it
defined in configuration.
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-pxa2xx.c

@@ -245,9 +245,13 @@ static void lpss_ssp_setup(struct driver_data *drv_data)
 	if (drv_data->master_info->enable_dma) {
 		__lpss_ssp_write_priv(drv_data, config->reg_ssp, 1);
 
-		value = __lpss_ssp_read_priv(drv_data, config->reg_general);
+		if (config->reg_general >= 0) {
+			value = __lpss_ssp_read_priv(drv_data,
+						     config->reg_general);
 			value |= GENERAL_REG_RXTO_HOLDOFF_DISABLE;
-		__lpss_ssp_write_priv(drv_data, config->reg_general, value);
+			__lpss_ssp_write_priv(drv_data,
+					      config->reg_general, value);
+		}
 	}
 }