media: atomisp: move atomisp_gmin_platform.c to pci/ dir

The atomisp_gmin_platform.c is not a platform driver anymore,
but it is, instead, part of the atomisp driver.

Move it to be together with the driver. As a bonus, as the
atomisp i2c drivers depends on its contents, probing them
should load automatically the atomisp core. This should
likely avoid some possible race conditions.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>