fix(stm32mp1): remove old regulator framework for ssp

Remove the old regulator files that are no more
available.

Signed-off-by: Lionel Debieve <lionel.debieve@foss.st.com>
Change-Id: Ib122e6a5b906e4a4b2ab529c6bdb0f6996704b79
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/254885


Reviewed-by: CITOOLS <MDG-smet-aci-reviews@list.st.com>
Reviewed-by: CIBUILD <MDG-smet-aci-builds@list.st.com>