arm: Rename STM32MP13x

CONFIG options must not use lower-case letter. Convert this and related
ones to upper case.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@foundries.io>