Use multiple linear segments to better interpolate the dBm
for the signal strength.
The table that converts from linear strength to dB was
empirically determinated with the help of a signal generator
(DTA-2111).
The entries from -35dBm to -22.5dBm were taken using just
the signal generator and the board.
For the entries from -36dBm to -51dBm, a 16 dB tap was used,
in order to extend its range.
Signals below to -51dBm are just linearly interpolated.
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Acked-by: Patrick Boettcher <pboettcher@kernellabs.com>
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