bfin: Move gpio support for bf54x and bf60x into the generic driver folder.

bfin: Move gpio support for bf54x and bf60x into the generic driver folder.

The gpio spec for bf54x and bf60x differ a lot from the old gpio driver for bf5xx.
A lot of machine macros are used to accomodate both code in one gpio driver.
This patch split the old gpio driver and move new gpio2 support to the generic
gpio driver folder.

- To enable gpio2 driver, macro CONFIG_ADI_GPIO2 should be defined in the board's
config header file.
- The gpio2 driver supports bf54x, bf60x and future ADI processors, while the
older gpio driver supports bf50x, bf51x, bf52x, bf53x and bf561.
- All blackfin specific gpio function names are replaced by the generic gpio APIs.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>