karo: config: prevent conversion of numerical value '1' in header files to 'y' by...

karo: config: prevent conversion of numerical value '1' in header files to 'y' by define2mk.sed

The script 'tools/scripts/define2mk.sed' converts all defines with the
value '1' to 'y' to facilitate conditional compilation in Makefiles.
Prepend a '0x' prefix to values of '1' which should be kept as
numbers.