MIPS: ath79: add QCA955X specific glue to ath79_device_reset_{set, clear}

The ath79_device_reset_* are causing BUG when
those are used on the QCA955x SoCs. The patch
adds the required code to avoid that.

Cc: Rodriguez, Luis <rodrigue@qca.qualcomm.com>
Cc: Giori, Kathy <kgiori@qca.qualcomm.com>
Cc: QCA Linux Team <qca-linux-team@qca.qualcomm.com>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/4948/
Signed-off-by: John Crispin <blogic@openwrt.org>