Change pmap_enter_quick() to use the vm_prot_t parameter introduced in
revision 1.179 to correctly set/clear execute permission on the mapping
it creates. Thus, mmap(2)ing a memory resident file will not result in
the file being mapped with execute permission when execute permission was
not requested.

Eliminate an unneeded Instruction Memory Barrier (IMB) in
pmap_enter_quick(). Since there was no previous (instruction) mapping
for the given virtual address prior to pmap_enter_quick(), there can be
no instructions from the given virtual address in the pipeline that need
flushing.

MFC after: 1 week