update ONIE gdisk types to 0x3000 and 0x3001

Change the base of the ONIE gdisk types to 0x3000 to avoid conflicts
with the existing MBR type 0x31 (reserved by IBM and Microsoft).

The GUID does not change, only the gdisk types

part name     old type       new type
ONIE-BOOT     0x3100         0x3000
ONIE-CONFIG   0x3101         0x3001