UPSTREAM: arm64: entry: Add macro for reading symbol addresses from the trampoline

commit b28a8eeb upstream.

The trampoline code needs to use the address of symbols in the wider
kernel, e.g. vectors. PC-relative addressing wouldn't work as the
trampoline code doesn't run at the address the linker expected.

tramp_ventry uses a literal pool, unless CONFIG_RANDOMIZE_BASE is
set, in which case it uses the data page as a literal pool because
the data page can be unmapped when running in user-space, which is
required for CPUs vulnerable to meltdown.

Pull this logic out as a macro, instead of adding a third copy
of it.

Bug: 215557547
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I1d11f54bb867a6312069bc3fae6f4ceb4ab1fd20