Bart Van Assche noted that currently there are more people using the
32gbit driver than there are people using the older one. So it might
make sense to finally make switch and default to the 32gbit driver.
Although qla-32gbit is mentioned in the README, but there wasn't really a
way to enable it sans editing the code.
This commit adds an ability to enable the driver by passing
`QLA_32GBIT=y` variable at build time.
