spi: nxp_s32: use instance-based DT macros

At present, many of the NXP S32 shim drivers do not make use of
devicetree instance-based macros because the NXP S32 HAL relies on an
index-based approach, requiring knowledge of the peripheral instance
index during both compilation and runtime, and this index might not
align with the devicetree instance index.

The proposed solution in this patch eliminates this limitation by
determining the peripheral instance index during compilation
through macrobatics and defining the driver's ISR within the shim
driver itself.

Signed-off-by: Manuel Argüelles <manuel.arguelles@nxp.com>