soc: arm: gigadevice: use common API headers

Stop relying on <soc.h> to access HAL APIs. Use generic, per-API headers
instead. Note that <soc.h> has been left as is for now, since ARM MPU
relies on a fragile chain of includes/type definitions.

This change should improve compilation efficiency, as we no longer pull
APIs that are not needed. A similar approach is followed by STM32
drivers.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>