GPIO: CREG: improve flexibility of hsdk-creg-gpio driver

CREG GPIO is a driver for weird soc-specific output ports, which are
controlled by some fields in memory mapped register.

Example:

31                 9        7        5           0   < bit number
|                  |        |        |           |
[     not used     | gpio-1 | gpio-0 | <-shift-> ]   < 32 bit register
                       ^        ^
                       |        |
                write 0x2 == set output to "1" (activate)
                write 0x3 == set output to "0" (deactivate)

As of tooday we only support fixed (hardcoded) bit per gpio line,
activate / deactivatei and shift values. Fix that by read them from
device tree to be able to use this driver for other boards.

Remove "hsdk" prefix from compatible string as this driver can be
used with different boards like HSDK, AXS101, AXS103, etc.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>