x86/boot: Drop xen_virt_end

x86/boot: Drop xen_virt_end

The calculation in __start_xen() for xen_virt_end is an opencoding of
ROUNDUP(_end, 2M).  This is __2M_rwdata_end as provided by the linker script.

This corrects the bound calculations in arch_livepatch_init() and
update_xen_mappings() to not enforce 2M alignment when Xen is not compiled
with CONFIG_XEN_ALIGN_2M.

Furthermore, since 52975142d154 ("x86/boot: Create the l2_xenmap[] mappings
dynamically"), there have not been extraneous mappings to delete, meaning that
the call to destroy_xen_mappings() has been a no-op.

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