hugetlbfs read() support

Support for reading from hugetlbfs files.  libhugetlbfs lets application
text/data to be placed in large pages.  When we do that, oprofile doesn't
work - since libbfd tries to read from it.

This code is very similar to what do_generic_mapping_read() does, but I
can't use it since it has PAGE_CACHE_SIZE assumptions.

[akpm@linux-foundation.org: cleanups, fix leak]
[bunk@stusta.de: make hugetlbfs_read() static]
Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Acked-by: William Irwin <bill.irwin@oracle.com>
Tested-by: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>