x86/build: limit #include-ing by asm-offsets.c

x86/build: limit #include-ing by asm-offsets.c

This file has a long dependencies list and asm-offsets.h, generated from
it, has a long list of dependents. IOW if any of the former changes, all
of the latter will be rebuilt, even if there's no actual change to the
generated file. Therefore avoid including headers we don't actually need
(generally or configuration dependent).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>