powerpc: mpc85xx: remove dead watchdog-related code

powerpc: mpc85xx: remove dead watchdog-related code

Nothing in-tree calls watchdog_reset() anymore (that stopped two years
ago with the removal of the WATCHDOG_RESET macro). So that function is
dead code.

That was the only caller of reset_85xx_watchdog(), so that
can obviously also be removed.

Finally, init_85xx_watchdog() is/was also not called from anywhere, so
that can go away as well, which nicely also removes a bit of
arch-specific code from the generic watchdog.h header.

Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Stefan Roese <sr@denx.de>