Some legacy devices support ony I2C standard mode at 100kHz.
This patch allows to select the standard mode through the DTS
with the use of the existing clock-frequency parameter.
When clock-frequency parameter is not set, the fast mode is selected.
Only when the parameter is set at 100000, the standard mode is selected.
Signed-off-by: Romain Baeriswyl <romainba@abilis.com> Reviewed-by: Christian Ruppert <christian.ruppert@abilis.com> Acked-by: Alan Tull <atull@opensource.altera.com> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>