ARM: multi_v7_defconfig: Enable support for STPMIC1

STPMIC1 is a PMIC from STMicroelectronics. The STPMIC1 integrates 10
regulators, 3 power switches, a watchdog and an input for a power on key.

Signed-off-by: Pascal Paillet <p.paillet@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Olof Johansson <olof@lixom.net>