gpio: stmpe: Add STMPE1600 support

The particularities of this variant are:
- GPIO_XXX_LSB and GPIO_XXX_MSB memory locations are inverted compared
  to other variants.
- There is no Edge detection, Rising Edge and Falling Edge registers.
- IRQ flags are cleared when read, no need to write in Status register.

Signed-off-by: Amelie DELAUNAY <amelie.delaunay@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>