i2c: uapi: add macro to describe support for all SMBus transfers

Some I2C bus master drivers which support I2C_M_RECV_LEN do not set
the functionality bits of the now supported SMBus transfers. Add a
convenience macro to make this very simple.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>