joypadtest: use joypad_get_rumble_supported instead of assuming a Rumble Pak

[zoncabe]

joypadtest never exercises rumble on a GameCube controller.

"e165fb5 gated joypad_get_rumble_supported behind whether a Rumble Pak was
attached, which obviously will never be true for a GameCube controller. The
whole point of joypad_get_rumble_supported is so you don't have to assume
which controller type is connected."

Both the activation block and the status line sit behind
accessory_type == JOYPAD_ACCESSORY_TYPE_RUMBLE_PAK, so with a GameCube
controller joypad_set_rumble_active is never called and the Rumble: line
never prints, even though rumble_method is JOYPAD_RUMBLE_METHOD_GCN_CONTROLLER
and the motor is available.

This switches both checks to rumble_supported, which covers the Rumble Pak and
the GameCube controller alike.

Tested against ares with gc controller support using an xbox controller: holding A now toggles the motor
and the status line reads Rumble: Active. Behaviour with a Rumble Pak on an
N64 controller is unchanged.

Opening this as a draft because the joypad_get_rumble_supported call that was
on line 115, inside the if on line 113, moved out of that if, and I'm not
sure what the consequences of that could be.