refactor(plat/st): rename OP-TEE pager to core

OPTEE_PAGER defines are renamed OPTEE_CORE.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I4c28d3b0a6ed843088a3ef06e3e348ce689fabde
2 files changed