i2c: add i2c deblock sequence before and after every mux config

To make sure that the mux can be configured a deblocking sequence
is done before the mux configuration. After the mux switch the new leaf
of, the i2c tree must be again deblocked.

Signed-off-by: Stefan Bigler <stefan.bigler@keymile.com>
Acked-by: Heiko Schocher <hs@denx.de>
cc: Wolfgang Denk <wd@denx.de>
cc: Detlev Zundel <dzu@denx.de>
cc: Prafulla Wadaskar <prafulla@marvell.com>
cc: Valentin Longchamp <valentin.longchamp@keymile.com>
cc: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>