[ARM] pxa: Add PXA support for PWM API

Patch mainly from Eric Miao, with minor edits by rmk.

Note: PWM0 and PWM2 share the same register I/O space and clock gating
on pxa{27x, 3xx}, thus PWM2 is treated in the driver as a child PWM of
PWM0. And this is also true for PWM1/3.

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/mach-pxa/Kconfig b/arch/arm/mach-pxa/Kconfig
index 5da7a68..9c01505 100644
--- a/arch/arm/mach-pxa/Kconfig
+++ b/arch/arm/mach-pxa/Kconfig
@@ -273,4 +273,9 @@
 	tristate
 	help
 	  Enable support for PXA2xx SSP ports
+
+config PXA_PWM
+	tristate
+	help
+	  Enable support for PXA2xx/PXA3xx PWM controllers
 endif