Replace usages of the locally defined ABS() macro with calls to the
canonical abs() from kernel.h and remove the old definitions of ABS()

This change was originally motivated by two local definitions of the
ABS (absolute value) macro that fail to parenthesize their parameter
properly. This can lead to a bad expansion for low-precedence
expression arguments.

For example: ABS(1-2) currently expands to ((1-2) < 0 ? (-1-2) : (1-2))
which evaluates to -3. But the correct expansion would be
((1-2) < 0 ? -(1-2) : (1-2)) which evaluates to 1.
Signed-off-by: Dan Gopstein <dgopstein@nyu.edu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>