pwm: atmel: add Timer Counter Block PWM driver

This patch adds a PWM driver based on Atmel Timer Counter Block. The
Timer Counter Block is used in Waveform generator mode.

A Timer Counter Block provides up to 6 PWM devices grouped by 2:
* group 0 = PWM 0 and 1
* group 1 = PWM 2 and 3
* group 2 = PMW 4 and 5

PWM devices in a given group must be configured with the same period
value. If a PWM device in a group tries to change the period value and
the other device is already configured with a different value an error
will be returned.

This driver requires device tree support. The Timer Counter Block number
used to create a PWM chip is given by the tc-block field in an
"atmel,tcb-pwm" compatible node.

This patch was tested on kizbox board (at91sam9g20 SoC) with pwm-leds.

Signed-off-by: Boris BREZILLON <linux-arm@overkiz.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 62a2963..94ba21e 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -1,5 +1,6 @@
 obj-$(CONFIG_PWM)		+= core.o
 obj-$(CONFIG_PWM_AB8500)	+= pwm-ab8500.o
+obj-$(CONFIG_PWM_ATMEL_TCB)	+= pwm-atmel-tcb.o
 obj-$(CONFIG_PWM_BFIN)		+= pwm-bfin.o
 obj-$(CONFIG_PWM_IMX)		+= pwm-imx.o
 obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o