p54: parse output power table

For the upcoming tpc changes, the driver needs
to provide sensible max output values for each
supported channel.

And while the eeprom always had a output_limit
table, which defines the upper limit for each
frequency and modulation, it was never really
useful for anything... until now.

Note: For anyone wondering about what your card
is calibrated for: check "iw list".
	* 2412 MHz [1] (18.0 dBm)
	* 2437 MHz [6] (19.0 dBm)
	[...]
	* 5180 MHz [36] (18.0 dBm)
	* 5260 MHz [52] (17.0 dBm) (radar detection)
	* 5680 MHz [136] (19.0 dBm) (radar detection)
(for a Dell Wireless 1450 USB Adapter)

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>