mfd: stmpe: Update DT support for stmpe driver

This patch extends existing DT support for stmpe devices. This updates:
- missing header files in stmpe.c
- stmpe_of_probe() with pwm, rotator and new bindings.
- Bindings are updated in binding document.

Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vipul Kumar Samar <vipulkumar.samar@st.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>