drm2: remove DRM_SPINXXX macros

* They did not apply 1:1 to DragonFly locking directives; keeping them
  in the drivers would have meant lockmgr locks would have had to be be
  used in situations where spinlocks could have done the job.

* Besides the obvious performance pessimization issues, they had the
  unfortunate effect of obscuring the source code

* The original DRM code in the Linux kernel doesn't even use them, they
  were purely a FreeBSD addition
drm2: Remove dubious AGP locks

They are not present in the original Linux code.
kernel: Add bitcount32 to sys/systm.h
kernel: Import pci_save_state and pci_restore_state from FreeBSD
acpica: Replace some include paths by full ones

To allow the ACPI header files to be used in the whole kernel