Simplify multiplications and divisions with constants when the
constant is 1 or -1.

When the constant is a power of 2, replace them by bit shits.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e53b1f4a4150ec6cabcaeeef82bf9c361b5f9204.1675245773.git.christophe.leroy@csgroup.eu