soc: imx: Break dependency on SOC_IMX8MQ for GPCv2

Since this is going to be used on more SoCs than just i.MX8MQ, make
the dependency here more generic by using ARCH_MXC instead.
Also remove the SOC_IMX7D since it is also included by the ARCH_MXC.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>