configs: BPI-R2: Disable EFI Grub workaround

The EFI Grub workaround on BananaPi R2 slows down the boot process to
the point, that the watchdog will trigger a reboot before the kernel can
reset it. Fix this by disabeling the workaround.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>