gpio: dwapb: Enable SPL support for DWAPB GPIO driver

gpio: dwapb: Enable SPL support for DWAPB GPIO driver

Add SPL_DWAPB_GPIO configuration option to enable the Designware APB
GPIO driver in SPL builds.

Changes:
- Add SPL_DWAPB_GPIO Kconfig option with SPL_DM_GPIO dependency
- Update Makefile to use CONFIG_$(PHASE_)DWAPB_GPIO pattern for
  conditional compilation in both SPL and main U-Boot builds

Signed-off-by: Tanmay Kathpalia <tanmay.kathpalia@altera.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Tom Rini <trini@konsulko.com>