xilinx_xiic: Fix transfer initialisation

Prior to starting a new transfer, conditionally wait for bus to not
be busy.

Reinitialise controller as otherwise operation is not stable.
For reference, see linux kernel
commit 9656eeebf3f1 ("i2c: Revert i2c: xiic: Do not reset controller before every transfer")

hs: Fixed DOS line endings
    added missing '\n'
    Fixed git commit description style

Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>