ArmPlatformPkg/Bds: Fixed condition on LOAD_OPTION_CATEGORY_BOOT

The condition tries to identify if we were starting a EFI
OS Loader or EFI Application.
But LOAD_OPTION_CATEGORY_BOOT was used as a mask to check the
attributes of the boot options while it is not a mask.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15900 6f19259b-4bc3-4df7-8a09-765794883524