loader: allow attempting more than one method of PCI identification.

loader: allow attempting more than one method of PCI identification.

loader_get_pci_id_for_fd() and loader_get_device_name_for_fd() now attempt
all available strategies to identify the hardware, instead of conditionally
compiling in a single test.  The existing libudev and DRM approaches have
been retained, attempting first libudev (if available) and then DRM (if
necessary).

Signed-off-by: Gary Wong <gtw@gnu.org>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>