rt2x00: rt2800lib: introduce RFCSR3_VCOCAL_EN

On the RF3290,RF5360,RF5370,RF5372,RF5390,RF5392
radio frontends, the VCO calibration can be
controlled via the RFCSR3 register. The current
code uses the RFCSR30_RF_CALIBRATION constant to
enable the calibration, however that belongs to
the RFCSR30 register. Although the values of the
constant is correct, but using that for another
register is confusing.

Add a new definition for the VCO calibration enable
bit of the RFCSR3 register and use that in the
relevant places in order to avoid confusions.

The patch contains no functional changes.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>