xen/arm: Move macro VABORT_GEN_BY_GUEST to common header

xen/arm: Move macro VABORT_GEN_BY_GUEST to common header

We want to move part of SErrors checking code from hyp_error assembly code
to a function. This new function will use this macro to distinguish the
guest SErrors from hypervisor SErrors. So we have to move this macro to
common header.

The VABORT_GEN_BY_GUEST macro uses the symbols abort_guest_exit_start
and abort_guest_exit_end. After we move this macro to a common header,
we need to make sure that the two symbols are visible to other source
files. Currently, they are declared .global in arm32/entry.S, but not
arm64/entry.S. Fix that.

Signed-off-by: Wei Chen <Wei.Chen@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>