MFC r361007, r361138-r361140, r361245-r361246

r361007:
linuxkpi: Add EBADRQC to errno.h

This is used in the amdgpu driver from Linux 5.2

Sponsored-by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D24807

r361138:
linuxkpi: Add atomic_dec_and_mutex_lock

This function decrement the counter and if the result is 0 it acquires
the mutex and returns 1, if not it simply returns 0.
Needed by DRM from Linux v5.3

Sponsored-by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D24847

r361139:
linuxkpi: Add __mutex_init

Same as mutex_init, the lock_class_key argument seems to be only used for
debug in Linux, simply ignore it for now.
Needed by DRM in Linux v5.3

Sponsored-by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D24848

r361140:
linuxkpi: Add offsetofend macro

This calculate the offset of the end of the member in the given struct.
Needed by DRM in Linux v5.3

Sponsored-by: The FreeBSD Foudation
Differential Revision: https://reviews.freebsd.org/D24849

r361245:
linuxkpi: Add __init_waitqueue_head

The only difference with init_waitqueue_head is that the name and the
lock class key are provided but we don't use those so use init_waitqueue_head
directly.

Sponsored-by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D24861

r361246:
linuxkpi: add pci_dev_present

pci_dev_present shows if a set of pci ids are present in the system.
It just wraps pci_find_device.
Needed by DRMv5.2

Submitted by: Austing Shafer (ashafer@badland.io)
Differential Revision: https://reviews.freebsd.org/D24796