mlxsw: reg: Add macro for getting QSFP module EEPROM page number

Provide a macro for getting QSFP module EEPROM page number from the
optional upper page number row offset, specified in request.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>