[WCNCR00146539] regd: add loading tx power limit from text file

[Description]
Add loading Tx power limit from text file
1. Remove load from binary related code
2. Parse Tx power limit from file "TxPwrLimit_MT76x8.dat"

[Test]
1. Use a fake TxPwrLimit_MT76x8.dat with US settings, run:
    i. iwpriv wlan0 driver "country US"
    ii. iw reg set US
   the settings are both correctly reflection in the TMAC
   frame power registers.
2. Without TxPwrLimit_MT76x8.dat file, the driver will not be affected

Change-Id: Ie680712fa2b0085bfc66193b93f722af7e15d6e7
Feature: regd
Signed-off-by: Awk Jiang <awk.jiang@mediatek.com>
CR-Id: WCNCR00146539
5 files changed