configs/orangepi_pc_defconfig: switch to extlinux

configs/orangepi_pc_defconfig: switch to extlinux

Changes:
* Switch to common orangepi scenario for multiple boards (board/orangepi/common) to create an SD image.
* Exclude FAT partition, it is no longer needed for U-Boot.
* Switch SD image from MBR to GPT for partition-uuid to work.
* Switch to extlinux, this is convenient for debugging.

Signed-off-by: Sergey Kuzminov <[email protected]>
Reviewed-by: Giulio Benetti <[email protected]>
Tested-by: Giulio Benetti <[email protected]>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <[email protected]>