Change pmap_enter(9) interface to take flags parameter and superpage
mapping size (currently unused).  The flags includes the fault access
bits, wired flag as PMAP_ENTER_WIRED, and a new flag
PMAP_ENTER_NOSLEEP to indicate that pmap should not sleep.

For powerpc aim both 32 and 64 bit, fix implementation to ensure that
the requested mapping is created when PMAP_ENTER_NOSLEEP is not
specified, in particular, wait for the available memory required to
proceed.

In collaboration with:	alc
Tested by:	nwhitehorn (ppc aim32 and booke)
Sponsored by:	The FreeBSD Foundation and EMC / Isilon Storage Division
MFC after:	2 weeks