Added regulators,GPIOs and changes required to power on/off wcn6750.
Added support for firmware download for wcn6750.

Changes done in detail:
1. Added regulators and corresponding current values.
2. Added sw_ctrl GPIO pin which is output from BT SoC and indicates
   status of clock supply to BT SoC.
3. Added inline function to check if the SoC type is wcn6750.
4. Modified the function qca_wcn3990_init() to support wcn6750 and
   renamed it to qca_regulator_init().
Signed-off-by: Venkata Lakshmi Narayana Gubba <gubbaven@codeaurora.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>