imx: re-work of PWM, add i.MX21 support

* Kconfig enables now HAVE_PWM (this enables in turn the selection of
  CONFIG_BACKLIGHT_PWM)
* changes CONFIG_ARCH_MXyy to CONFIG_MACH_MXyy
* fix some register names to match those of the reference manual
* write a stub code so that the PWM can be used to program the
  LCD backlight
* convert from #ifdef CONFIG_ARCH_MXxx to cpu_is_mxXX()
* remove unneeded defines and fix 80-column "violations" of checkpatch.pl

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
diff --git a/arch/arm/plat-mxc/Kconfig b/arch/arm/plat-mxc/Kconfig
index 61acd4c..beeb01a 100644
--- a/arch/arm/plat-mxc/Kconfig
+++ b/arch/arm/plat-mxc/Kconfig
@@ -48,6 +48,7 @@
 config MXC_PWM
 	tristate "Enable PWM driver"
 	depends on ARCH_MXC
+	select HAVE_PWM
 	help
 	  Enable support for the i.MX PWM controller(s).