libxl: cleanup some misuse of 'cpumap' as parameter

libxl: cleanup some misuse of 'cpumap' as parameter

in favour of the more generic 'bitmap', which is better
since these are generic libxl_bitmap_* functions.

Also fix a typo, and remove a stale (and wrong) comment.

No functional change intended.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>