ARM: dts: sun8i: tbs-a711: Add node for BMA250 accelerometer

A711 tablet has BMA250 accelerometer connected to I2C1 bus. Enable
both the I2C1 bus and add the accelerometer device to it.

Signed-off-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>