eal: forbid loading drivers from insecure paths

eal: forbid loading drivers from insecure paths

Any paths on the system which are world-writable are insecure and should
not be used for loading drivers. Therefore, whenever an absolute or
relative driver path is passed to EAL, check for world-writability and
don't load any drivers from that path if it is insecure. Drivers loaded
from system locations i.e. those passed without any path info and found
automatically by the loader, are excluded from these checks as system paths
are assumed to be secure.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>