[ARM] pxa: add generic PWM backlight driver

Patch mostly from Eric Miao, with minor edits by rmk to convert
Eric's driver to a generic PWM-based backlight driver.

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

include/linux/pwm_backlight.h

@@ -0,0 +1,14 @@
+/*
+ * Generic PWM backlight driver data - see drivers/video/backlight/pwm_bl.c
+ */
+#ifndef __LINUX_PWM_BACKLIGHT_H
+#define __LINUX_PWM_BACKLIGHT_H
+
+struct platform_pwm_backlight_data {
+	int pwm_id;
+	unsigned int max_brightness;
+	unsigned int dft_brightness;
+	unsigned int pwm_period_ns;
+};
+
+#endif