ARM Packages: use GCC_ASM_EXPORT to export functions

ARM Packages: use GCC_ASM_EXPORT to export functions

This ensures the .type directive is used to mark them as function symbols

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Brendan Jackman <brendan.jackman@arm.com>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15506 6f19259b-4bc3-4df7-8a09-765794883524