libdm: implement dm_percent_to_round_float

libdm: implement dm_percent_to_round_float

Add function to adjust printing of percent values in better way.
Rounding here is going along following rules:

0% & 100% are always clearly reported with  .0 decimal points.

Values slightly above 0% we make sure a nearest bigger
non zero value with given precission is printed
(i.e. 0.01  for  %.2f  will be shown)

For values closely approaching 100% we again detect and adjust value
that is less then 100 when printed.
(i.e. 99.99  for %.2f will be shown).

For other values we are leaving them with standard rounding mechanism
since we care mainly about corner values 0 & 100 which need to be
printed precisely.