chain: Fix chainloading on 6.02

My commit 09f4ac33 broke 'com32/lib/syslinux/disk.c'

__lowmem doesn't work for declarations outside the core.
Using __lowmem outside the core wouldn't have the desired effect, then lmalloc
must be used instead to store dapa into the correct section (".lowmem").

Reported-by: Dark Raven <drdarkraven@gmail.com>
Signed-off-by: Raphael S. Carvalho <raphael.scarv@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
core: don't leak the __lowmem and __bss16 macros to modules

The __lowmem and __bss16 macros are only useful in the core itself.
Hide them from modules so people don't use them by mistake.

extern declarations don't need them (and are safe in modules), they
are only necessary at the point of definition (which must be in the
core.)

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>