driver/ifc: replace __ilog2 with LOG2 macro

driver/ifc: replace __ilog2 with LOG2 macro

Replaces __ilog2 function call with LOG2 macro, required to
use macros in global variables.

Also, corrects the value passed in LOG2 for some PowerPC
platforms. Minimum value that can be configured is is 64K
for IFC IP.

Signed-off-by: Pankit Garg <[email protected]>
Signed-off-by: Rajesh Bhagat <[email protected]>
[YS: fix white space around operator]
Reviewed-by: York Sun <[email protected]>