The user access functions may generate a fault, resulting in invocation
of a handler that may sleep.

This patch annotates the accessors with might_fault() so that we print a
warning if they are invoked from atomic context and help lockdep keep
track of mmap_sem.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>