dt-bindings: net: nxp,s32-dwmac: Use the GPR syscon

dt-bindings: net: nxp,s32-dwmac: Use the GPR syscon

The S32 chipsets have a GPR region which has a miscellaneous registers
including the GMAC_0_CTRL_STS register.  Originally, this code accessed
that register in a sort of ad-hoc way, but it's cleaner to use a
syscon interface to access these registers.

We still need to maintain the old method of accessing the GMAC register
but using a syscon will let us access other registers more cleanly.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/3b75e950b2f8faecd1a9fa757e7eb7b42ace838f.1769764941.git.dan.carpenter@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>