NVMe: Add a few calling convention notes
NVMe: Add a few calling convention notes

For the benefit of reviewers, add comments to a few functions describing
their calling context

Signed-off-by: Matthew Wilcox <ed1245e46949b7b8f2bca25d41520ebc8aeefcf8@intel.com>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs