Introduce new, low level GPIO initialization code

Introduce new, low level GPIO initialization code

New code is universal and allows to predefine several config options:
- JTAG enable
- bitmasks for GPIOs set as inputs and outputs
- bitmasks for GPIO driven LEDs (active in low and hi)
- bitmasks for initial values on configured GPIOs
- LSUART GPIO lines

Code was tested on all supported WiSoCs: AR933x, AR934x and QCA95xx.

This commit removes also old GPIO related code and adds needed
bitmasks definitions in ap121 and db12x configs.