linuxkpi: Move lkpi_pcim_iomap_devres_find to .c file

lkpi_pcim_iomap_devres_find encodes the size of struct pcim_iomap_devres
in the code, so move from .h to .c to move from client driver to
linuxkpi module.

Sponsored by: Netflix
Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D34775