pwm: pwm-mxs: use global reset function stmp_reset_block

Use global reset function stmp_reset_block instead of mxs_reset_block
to remove <mach/common.h> inclusion.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>