EmbeddedPkg: Add EFIAPI to several Ebl functions

The EFIAPI function declaration is missing for several functions in the
EmbeddedPkg/Ebl directory. A few function pointer struct members expect
EFIAPI though and GCC46/X64 will fail to compile the directory without
them.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Thomas Palmer <thomas.palmer@hpe.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18697 6f19259b-4bc3-4df7-8a09-765794883524