nvme: Use the Maximum Queue Entries Supported (MQES) to initialize I/O queues

nvme: Use the Maximum Queue Entries Supported (MQES) to initialize I/O queues

Use the Maximum Queue Entries Supported (MQES) to initialize I/O queues
depth rather than picking a fixed number (256) which might not be
supported by some NVMe controllers (the NVMe specification says that an
NVMe controller may support any number between 2 to 4096).

Still cap the I/O queues depth to 256 since, during my testing, SeaBIOS
was running out of memory when using something higher than 256 (4096 on
the NVMe controller that I've had a chance to try).

Signed-off-by: Filippo Sironi <sironi@amazon.de>