x86/config: Fix warning for 'make ARCH=x86_64 tinyconfig'

x86/config: Fix warning for 'make ARCH=x86_64 tinyconfig'

Kconfig emits a warning for the following command:

  $ make ARCH=x86_64 tinyconfig
  ...
  .config:1380:warning: override: UNWINDER_GUESS changes choice state

When X86_64=y, the unwinder is exclusively selected from the following
three options:

 - UNWINDER_ORC
 - UNWINDER_FRAME_POINTER
 - UNWINDER_GUESS

However, arch/x86/configs/tiny.config only specifies the values of the
last two. UNWINDER_ORC must be explicitly disabled.

Signed-off-by: Masahiro Yamada <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]