uaccess: Define pagefault lock guard

Define a pagefault lock guard which allows to simplify functions that
need to disable page faults.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
Link: https://lore.kernel.org/r/8a01beb0b671923976f08297d81242bb2129881d.1750917800.git.vmalik@redhat.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>