docs(maintainers): update missing files related to EL3 SPMC

Few header files are added to the list maintained by EL3 SPMC
code owner.

Also added missing copyright license footer message.

Change-Id: I72afe4c4e1280ef64610a5efe6d1b0e2c9727bb0
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
1 file changed