ArmPlatformPkg/Bds: Added support for booting legacy kernel from BDS

ArmPlatformPkg/Bds: Added support for booting legacy kernel from BDS

When PcdBdsLinuxSupport is enabled, users can create boot
entries for the legacy EFI Linux loader.

The ARM BDS detects if the image is a EFI image if not
then it assumes it is a legacy Linux kernel (a kernel
without EFI Stub).
If the Boot Manager did not manage to load the binary
(it could happen when the binary is on the network or
not present on the media yet).

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@17974 6f19259b-4bc3-4df7-8a09-765794883524