eal/linux: only call iopl on x86

eal/linux: only call iopl on x86

From iopl(2) man page: "This call is mostly for the x86 architecture. On
many other architectures it does not exist or will always return an
error".

This patch removes the call to iopl() in rte_eal_iopl_init() for
architectures other than x86, and always return 0 (success). This was
already done for ARM in
commit 0291476ae364 ("eal/linux: never check iopl for arm")

Next patches will introduce the support of memory mapped IO resources
for architectures != x86.

On BSD, there is nothing to do as open("/dev/io") already does the
proper thing. See man IO(4).

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>