stm32mp1: configure wakeup interrupt for non-secure software

The wakeup from STOP mode should be available even if TZEN bit is 0 in RCC.

Change-Id: I4301ebf76d4a48972bfc2c3d14945a7c18249b51
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/138474


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: CIBUILD <smet-aci-builds@lists.codex.cro.st.com>
Reviewed-by: Lionel DEBIEVE <lionel.debieve@st.com>
Tested-by: Lionel DEBIEVE <lionel.debieve@st.com>