<sys/slaballoc.h>: Switch to lighter <sys/_malloc.h> header.

<sys/slaballoc.h>: Switch to lighter <sys/_malloc.h> header.

 The <sys/globaldata.h> embeds SLGlobalData that in turn embeds the
 "struct malloc_type".  Adjust several kernel sources for missing
 includes where memory allocation is performed.  Try to use alphabetical
 include order.

 Now (in most cases) <sys/malloc.h> is included after <sys/objcache.h>.
 Once it gets cleaned up, the <sys/malloc.h> inclusion could be moved
 out of <sys/idr.h> to drm Linux compat layer linux/slab.h without side
 effects.