designware_i2c: disable i2c controller during target address setup

designware_i2c: disable i2c controller during target address setup

As it is stated in DesignWare I2C databook: writes to IC_TAR (0x4)
register succeed only when IC_ENABLE[0] is set to 0.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Tom Rini <trini@ti.com>
cc: Armando Visconti <armando.visconti@st.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Cc: Heiko Schocher <hs@denx.de>
Cc: Vipin KUMAR <vipin.kumar@st.com>
Cc: Tom Rix <Tom.Rix@windriver.com>
Cc: Mischa Jonker <mjonker@synopsys.com>