doc: move VFIO driver to be first in Linux guide
doc: move VFIO driver to be first in Linux guide

Currently, the Linux GSG mentions UIO drivers first. This is not ideal
as for the longest time, the recommended way to use DPDK with hardware
devices has been to use VFIO driver.

This commit simply moves UIO section after VFIO, with minor edits.

Signed-off-by: Anatoly Burakov <814e00d8f6e4e81b7ccc7e3e5a0bfec0078f0203@intel.com>
Reviewed-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk