clk: MediaTek: add hifsys entry for MT7623 SoC.

This adds high speed interface subsystem - hifsys (i.e. PCIe and USB)
for MT7623 SoC and enables its reset controller.

The control block is shared with ethsys and accordingly rename the
related defines.

Tested-by: Frank Wunderlich <frank-w@public-files.de>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>