ArmPkg/BdsLinuxFdt.c: Split PrepareFdt() into several functions.

ArmPkg/BdsLinuxFdt.c: Split PrepareFdt() into several functions.

PrepareFdt() function was getting pretty fat and big functions are more
complex to understand and find the information one is looking for.

This patch extracts some code from PrepareFdt() function and put it
in some new functions.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14349 6f19259b-4bc3-4df7-8a09-765794883524