ANDROID: Split x86 and arm64 DDK headers.

The ddk_headers targets should be architecture specific; that
is, an x86_64 ddk_module should not be able to see arm64 headers,
and vice versa.

Since the majority of devices is arm64, the //common:all_headers
alias points to //common:all_headers_aarch64. x86_64 devices
can use //common:all_headers_x86_64 instead.

After this change:

- arm64 ddk_modules can continue depending on //common:all_headers, or
  they can depend on //common:all_headers_aarch64 to be explicit.
  In this case, they will not see the x86 headers.
- x86 ddk_modules can depend on //common:all_headers_x86_64.
  In this case, they will not see the arm64 headers.
- unsafe headers under drivers/ are not splitted; they aren't arch specific.

This change ensures that e.g. virtual_device_x86_64 does not
search the headers from the arm64 folders.

Test: bazel build //common:all_headers
Test: bazel build --allow_ddk_unsafe_headers_set //common:all_headers
Bug: 256225968
Signed-off-by: Yifan Hong <elsk@google.com>
Change-Id: I80dd33fb4c0e93dcba3e0714f9fd67d78596ab15