mfd: stmpe: Use generic bit mask name

In order to prepare the ground to STMPE1600,
as STMPE1600's SYS_CTRL register has the same layout as
STMPE801 variant, unify STMPExxx_REG_SYS_CTRL_RESET/INT_EN/INT_HI
bit masks to more generic STMPE_SYS_CTRL_RESET/INT_EN/INT_HI

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