package/oprofile: introduce a BR2_PACKAGE_OPROFILE_ARCH_SUPPORTS

operf_utils.h defines rmb() for a limited number of architectures, so
add this list to BR2_PACKAGE_OPROFILE_ARCH_SUPPORTS to disable any new
or unsupported architectures.

Doing so, this disable oprofile for m68k which lack of memory barrier
operations.

Remove nios2 dependency since it's not supported by oprofile even if
binutils could be built for nios2.

Fixes:

 http://autobuild.buildroot.net/results/1cc761d8a5715d0a2c6eaacfde7e44b225da1b36



Signed-off-by: Romain Naour <romain.naour@gmail.com>
[Thomas: remove BR2_sh64, use BR2_sh instead of BR2_sh4.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>