x86/shadow: replace stale literal numbers in hash_{vcpu,domain}_foreach()

x86/shadow: replace stale literal numbers in hash_{vcpu,domain}_foreach()

15 apparently once used to be the last valid type to request a callback
for, and the dimension of the respective array. The arrays meanwhile are
larger than this (in a benign way, i.e. no caller ever sets a mask bit
higher than 15), dimensioned by SH_type_unused. Have the ASSERT()s
follow suit and add build time checks at the call sites.

Also adjust a comment naming the wrong of the two functions.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>