ArmPlatformPkg: Remove Linux specific boot path

ArmPlatformPkg: Remove Linux specific boot path

PcdDefaultBootType has been removed when the embedded
Linux Loader has been removed from BdsLib.
The boot arguments (defined by PcdDefaultBootArgument)
are now always targetting EFI applications.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <Olivier.Martin@arm.com>
Reviewed-by: Ronald Cron <Ronald.Cron@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17971 6f19259b-4bc3-4df7-8a09-765794883524