apm821xx: move CONFIG_REGULATOR to target config

apm821xx: move CONFIG_REGULATOR to target config

This moves CONFIG_REGULATOR to the target config instead of the
subtarget config.

For kernel 5.10, CONFIG_AT803X_PHY depends on CONFIG_REGULATOR.
As we do not have a size constraint, move this symbol to the
target configuration for kernel 5.4 as well as 5.10.

Reported-by: Russell Senior <[email protected]>
Signed-off-by: David Bauer <[email protected]>