arm64: dts: mt7622: Drop the general purpose timer node

MediaTeks general purpose timer register into system in early phase
during kernel boot, but the clock sources aren't probed at this point.

The system has the ARM architecture timer, so we don't need the GPT
timer from mediatek. Drop the DT node for it.

Fixes: 9cc7f0de ("arm64: dts: mt7622: add timer, CCI-400 and PMU nodes")
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
[mb: fix commit message]
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>