net: dsa: mt7530: use unlocked regmap accessors

Instead of wrapping the locked register accessor functions, use the
unlocked variants and add locking wrapper functions to let regmap
handle the locking.

This is a preparation towards being able to always use regmap to
access switch registers instead of open-coded accessor functions.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>