x86: unilaterally remove .init mappings

x86: unilaterally remove .init mappings

Because of the new 2M alignment of .init and .bss, the existing memory
guarding infrastructure causes a shattered 2M superpage with non-present
entries for .init, and present entries for the alignment space.

Do away with the difference in behaviour between debug and non-debug builds;
always destroy the .init mappings, and reuse the space for xenheap.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <JBeulich@suse.com>