Refactor common patches

[drbild]

U-Boot, AT91Bootstrap, and other patches that are common across boards should be refactored into a shared subdirectories.

• [x] patches adding defconfigs can go in the global patches directory
• [x] patches with specific changes common for all router cards can go in boards/xaprc-common/patches.
• [x] patches specific to a specific board should stay in the board-specific patches directories.