NVMe: Update BAR structure to match the current spec

Add two reserved registers in the middle of the BAR to match the 1.0
spec plus ECN 0002.

Also rename IMC and ISC to INTMC and INTSC to conform with the spec.
We still don't need to use them :-)

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>