net: ethernet: mtk_eth_soc: convert clock bitmap to u64

The to-be-added MT7988 SoC adds many new clocks which need to be
controlled by the Ethernet driver, which will result in their total
number exceeding 32.
Prepare by converting clock bitmaps into 64-bit types.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://lore.kernel.org/r/6960a39bb0078cf84d7642a9558e6a91c6cc9df3.1690246066.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>