net/ena: disable readless communication when no HW support

net/ena: disable readless communication when no HW support

Depending on HW revision readless communcation between host and device
may be unavailable. In that case prevent PMD from setting up readless
communication mechanism.

"readless" refers to ability to read ENA registers without actually
issuing read request from host (x86). Instead, host programs 2 registers
on the device that triggers a DMA from device to host and reports a
register value. However, this functionality is not going to be available
in all types of devices. The decision if this mode is supported or not,
is taken from revision_id in pci configuration space.

Signed-off-by: Alexander Matushevsky <matua@amazon.com>
Signed-off-by: Jakub Palider <jpa@semihalf.com>
Signed-off-by: Jan Medala <jan@semihalf.com>