clk: mediatek: mt7988: rename TOPCKGEN factor clock to upstream naming

Rename TOPCKGEN factor clock to upstream neaming.
Upstream kernel linux reference the factor clock for apmixedpll with the
"pll" suffix. Align the naming to the upstream naming format in
preparation for OF_UPSTREAM support.

Also rename rtc clock to drop the CB_ as upstream doesn't have that.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>