FROMGIT: asm-generic: export: Stub EXPORT_SYMBOL with __DISABLE_EXPORTS

It is currently possible to stub EXPORT_SYMBOL() macros in C code using
__DISABLE_EXPORTS, which is necessary to run in constrained environments
such as the EFI stub or the decompressor. But this currently doesn't
apply to exports from assembly, which can lead to somewhat confusing
situations.

Consolidate the __DISABLE_EXPORTS infrastructure by checking it from
asm-generic/export.h as well.

Signed-off-by: Quentin Perret <qperret@google.com>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210203141931.615898-2-qperret@google.com
(cherry picked from commit 54effa65
 git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm.git

 next)
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I31d29e667d73f125b2de77247b6115c407e763b3
Bug: 178098380
Test: atest VirtualizationHostTestCases on an EL2-enabled device