mfd: stmpe: Add reset support for all STMPE variant

Reset was only implemented for STMPE1801 variant despite
all variant have a SOFT_RESET bit.

For STMPE2401/2403/801/1601/1801 SOFT_RESET bit is bit 7
of SYS_CTRL register.
For STMPE610/811 (which have the same variant id) SOFT_RESET
bit is bit 1 of SYS_CTRL register.

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