loader: Move non-error message to debug level

loader: Move non-error message to debug level

Currently when running mesa on imx6 the following loader warnings
are seen:

# kmscube -D /dev/dri/card1
MESA-LOADER: device is not located on the PCI bus
MESA-LOADER: device is not located on the PCI bus
MESA-LOADER: device is not located on the PCI bus
Using display 0x1920948 with EGL version 1.4

As this is not an error message, change it to debug level in
order to have a cleaner log output.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>