bus/pci: support I/O port operations with musl

bus/pci: support I/O port operations with musl

Add a fallback for non-GNU libc systems like musl libc for the
non-standard functions outl_p, outw_p and outb_p.

It solves the following errors when building with musl libc:
	pci_uio.c: undefined reference to 'outw_p'
	pci_uio.c: undefined reference to 'outl_p'
	pci_uio.c: undefined reference to 'outb_p'

Bugzilla ID: 35
Fixes: 756ce64b1ecd ("eal: introduce PCI ioport API")
Cc: stable@dpdk.org
Reported-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: David Marchand <david.marchand@redhat.com>