clk: mediatek: mt7622: add missing A1/2SYS clock ID

Add missing A1/2SYS clock ID just as a reference for OF_UPSTREAM
support. These clocks are not defined and are not usable as current
clock topckgen OPs doesn't support gates.

These special node won't ever be used by uboot hence just add them for
reference.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Tested-by: Frank Wunderlich <frank-w@public-files.de>