Split mlxplat_init() into two by adding mlxplat_pre_init().

Motivation is to prepare 'mlx-platform' driver to support systems
equipped PCIe based programming logic device.

Such systems are supposed to use different system resources, thus this
commit separates resources allocation related code.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Michael Shych <michaelsh@nvidia.com>
Link: https://lore.kernel.org/r/20230208063331.15560-7-vadimp@nvidia.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>