signal/arm64: Expand __do_user_fault and remove it

Not all of the signals passed to __do_user_fault can be handled
the same way so expand the now tiny __do_user_fault in it's callers
and remove it.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>