b43: HT-PHY: define regs for power estimation

In MMIO dumps of ndiswrapper there are following PHY ops:
phy_read(0x0118) -> 0x013d
phy_read(0x01ed) -> 0x993d
phy_read(0x0119) -> 0x012f
phy_read(0x01ee) -> 0x992f
phy_read(0x011a) -> 0x0139
phy_read(0x0969) -> 0x9939
It matches the code of wlc_phy_txpower_est_power_nphy (from brcm80211),
so we know the registers meaning.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>