refactor(drivers/marvell/comphy-3700): drop _REG prefixes and suffixes

Some register constants are defined with _REG suffix or REG_ prefix, but
others are not. Unify this by dropping these prefixes / suffixes.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Change-Id: I1ba331c0a4686093ee250bcaf3297349956ac9a8
2 files changed