arm64: opcodes.h: Add arm big-endian config options before including arm header

arm and arm64 use different config options to specify big endian. This
needs taking into account when including code/headers between the two
architectures.

A case in point is PAN, which uses the __instr_arm() macro to output
instructions. The macro comes from opcodes.h, which lives under arch/arm.
On a big-endian build the mismatched config options mean the instruction
isn't byte swapped correctly, resulting in undefined instruction exceptions
during boot:

| alternatives: patching kernel code
| kdevtmpfs[87]: undefined instruction: pc=ffffffc0004505b4
| kdevtmpfs[87]: undefined instruction: pc=ffffffc00076231c
| kdevtmpfs[87]: undefined instruction: pc=ffffffc00076231c
| kdevtmpfs[87]: undefined instruction: pc=ffffffc00076231c
| kdevtmpfs[87]: undefined instruction: pc=ffffffc00076231c
| kdevtmpfs[87]: undefined instruction: pc=ffffffc00076231c
| kdevtmpfs[87]: undefined instruction: pc=ffffffc00076231c
| kdevtmpfs[87]: undefined instruction: pc=ffffffc00076231c
| kdevtmpfs[87]: undefined instruction: pc=ffffffc00076231c
| kdevtmpfs[87]: undefined instruction: pc=ffffffc00076231c
| Internal error: Oops - undefined instruction: 0 [#1] SMP
| Modules linked in:
| CPU: 0 PID: 87 Comm: kdevtmpfs Not tainted 4.1.16+ #5
| Hardware name: Hisilicon PhosphorHi1382 EVB (DT)
| task: ffffffc336591700 ti: ffffffc3365a4000 task.ti: ffffffc3365a4000
| PC is at dump_instr+0x68/0x100
| LR is at do_undefinstr+0x1d4/0x2a4
| pc : [<ffffffc00076231c>] lr : [<ffffffc0000811d4>] pstate: 604001c5
| sp : ffffffc3365a6450

Cc: <stable@vger.kernel.org> #4.3.x-
Reported-by: Hanjun Guo <guohanjun@huawei.com>
Tested-by: Xuefeng Wang <wxf.wang@hisilicon.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>