Handle Common Platform Patches to support various boards

Ticket:
Reviewed By: Curt, Dustin
Testing Done:
Test:
1) Validated the script with unit tests
2) Built ONIE for both old and new patch layouts.

Changes:
1) Build Infrastructure is modified to support common patches for boards which has
   same platform i.e. p2020 based platforms.
2) Detailed Description:
   a) Platform specific u-boot and kernel patches for various boards will be maintained under
      MACHINEROOT directory.
   b) Board specific uboot and kernel patches will be maintained under MACHINE directory
   c) Infrastructure is modified to merge all these patches during the build process