Move android_filesystem_config.h => fs_config.h

The non AID_ things in android_filesystem_config.h are moved
to fs_config.h. For libcutils.vendor and libcutils_headers.vendor,
fs_config.h is not exported.

An empty system/core/include/private/fs_config.h is placed to
appease the dependency from certain modules (logd, etc.)
that includes system/core/include/private/android_filesystem_config.h
directly.

Test: m -j
Test: BOARD_VNDK_VERSION=current m -j
Bug: 63135587
Change-Id: I95dfb874a426941022b100c0ca26a0576b0f4aa3
Merged-In: I95dfb874a426941022b100c0ca26a0576b0f4aa3