oprofile: cleanup the style of the OPROFILE_BINARIES definition

There is no need to repeat OPROFILE_BINARIES += many times to add more
values to the variable. Just define it once with all the values, as we
do everywhere else in Buildroot.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>