ArmPkg/BdsLib: Added support to change the given DevicePath of a Boot Entry

ArmPkg/BdsLib: Added support to change the given DevicePath of a Boot Entry

Some boot entries might not have a EFI Device Path FilePath
attached to it (eg: EFI device Path for removable device path).
This patch allows a support loader to edit the EFI Device Path
and for instance add \EFI\BOOT\BOOT(ARM|AA64).EFI

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@16930 6f19259b-4bc3-4df7-8a09-765794883524