clk: stm32mp1_clk: restore IWDG APB clocks

In case of SP_MIN in DDR, the wrapper in BL2 uses the
iwdg clock for a watchdog refresh. Because it uses the
BL2 stacks, the clock counter is not correct and the
watchdog clocks are not properly restored.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: Iede2c00de80d0031b178d897c5e14fe47a7dad6d
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/188651


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: CIBUILD <smet-aci-builds@lists.codex.cro.st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>