arm: sunxi: h6: fix reset using r_wdog

Some H6 boards have a watchdog which didn't make the SoC
reboot properly.

Reason is still unknown but several people have test it.
Chen-Yu Tsai :
Pine H64 = H6 V200-AWIN H6448BA 7782 => OK
OrangePi Lite 2 = H6 V200-AWIN H8068BA 61C2 => KO

Martin Ayotte :
Pine H64 = H8069BA 6892 => OK
OrangePi 3 = HA047BA 69W2 => KO
OrangePi One Plus = H7310BA 6842 => KO
OrangePi Lite2 = H6448BA 6662 => KO

Clément Péron:
Beelink GS1 = H6 V200-AWIN H7309BA 6842 => KO

After the series of result, Icenowy try to reach Allwinner about this
issue but they seems not interested to investigate it.

As we don't have the ARIS coproc to do power management and watchdogis
the only solution to reset the board.

So, Change from watchdog to R_watchdog to allow a reboot on all H6
boards.

Signed-off-by: Clément Péron <peron.clem@gmail.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>