configs: da850evm: Remove DM_I2C_COMPAT

Since using DM_I2C_COMPAT throws a warning during compilation,
and it isn't really needed any longer, so this patch removes
this feature and shrinks the code a bit.

from:
   text	   data	    bss	    dec	    hex	filename
 343326	  13388	 123448	 480162	  753a2	u-boot

to:
   text	   data	    bss	    dec	    hex	filename
 342924	  13380	 123440	 479744	  75200	u-boot

Signed-off-by: Adam Ford <aford173@gmail.com>