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.

Approved by: re@ (gjb)
Sponsored by: Netflix
Reviewed by: hselasky, emaste
Differential Revision: https://reviews.freebsd.org/D34772

(cherry picked from commit 3ea682e21eed92f31dcfb8a34409580d36c452f7)
(cherry picked from commit 2cd55de380d3d6f02c9b40ea53a319b477268f1c)