ath9k: consistently use get_eeprom_rev(ah)

The AR5416_VER_MASK macro does the same as get_eeprom_rev, except that
one has to know the actual EEPROM type (and providing a reference to
that in a variable named "eep"). Additionally the eeprom_*.c
implementations used the same shifting logic multiple times to get the
eeprom revision which was also unnecessary duplication of
get_eeprom_rev.

Also use the AR5416_EEP_VER_MINOR_MASK macro where needed and introduce
a similar macro (AR5416_EEP_VER_MAJOR_MASK) for the major version.
Finally drop AR9287_EEP_VER_MINOR_MASK since it simply duplicates the
already defined AR5416_EEP_VER_MINOR_MASK.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>