cam: Make <cam/scsi/scsi_all.h> more self-contained

Include <sys/malloc.h> in the kernel for struct malloc_type.

Reviewed by: ken, imp
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D42205

(cherry picked from commit 2e539c6f5aba657c69790d91130ceceeb0b8c38e)