KVM: arm64: Don't use cbz/adr with external symbols

allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
linker errors:

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):
  relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0):
  relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

This is because with LTO, the compiler ends up placing hyp_panic()
more than 1MB away from __guest_enter(). Use an unconditional branch
and adr_l instead to fix the issue.

Link: https://github.com/ClangBuiltLinux/linux/issues/1317


Reported-by: Nathan Chancellor <nathan@kernel.org>
Suggested-by: Marc Zyngier <maz@kernel.org>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Will Deacon <will@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210305202124.3768527-1-samitolvanen@google.com