linuxkpi: Move lkpi_pci_devres_get_alloc into .c file

lkpi_pci_devres_get_alloc encodes the struct pci_devres into its
code. Move from .h file to .c file to move this knowledge into linuxkpi
module.

Sponsored by: Netflix
Reviewed by: hselasky, emaste
Differential Revision: https://reviews.freebsd.org/D34772