ANDROID: GKI: explicit include of stringify.h

The android_kabi.h header file uses the __stringify() macro without
explicitly including its definition via linux/stringify.h. This can
result in build breaking when using the ANDROID_KABI_USE macro:

  common/include/linux/ipv6.h:83:2: error: expected ')'
  ANDROID_KABI_USE(1, struct { __s32 accept_ra_min_lft; u32 padding; });
  ^
  [...]
  common/include/linux/android_kabi.h:44:24: note: expanded from macro '__ANDROID_KABI_CHECK_SIZE_ALIGN'
      __FILE__ ":" __stringify(__LINE__) ": "          \
                   ^

To fix this let android_kabi.h include stringify.h explicitly instead of
relying on includes of previous unrelated header files.

Bug: 330729479
Bug: 324437514
Change-Id: I16cced44e723871b2e1a92b312e60f38e41fea70
Signed-off-by: Carlos Llamas <cmllamas@google.com>