Configure ld.config.txt for SP-HALs

Now, framework process (any process that is executing /system/bin/* or
/system/xbin/*) are started with three namespaces; default, sphal and
vndk.

default namespace is the namespace that is responsible for loading libs
from /system/lib. It can't load libs from other places such as
/vendor/lib. (However, we temporarily open the path since we haven't
finished the system partition cleanup, but will do eventually).

sphal namespace is the namespace where SP-HAL (Same-process HAL) is
loaded. SP-HAL are the only vendor libraries that are allowed to be
loaded inside framework processes. libEGL_<chipset>.so and
android.hardware.graphics.mapper@2.0-impl.so, etc are SP-HALs. When
framework needs to load those SP-HALs, it explicitly loads it from this
namespace using android_get_exported_namespace() and
android_dlopen_ext().

vndk namespace is the namespace for loading vndk-sp (Vendor-NDK for
Same-Process) libs, which is a small set of framework libraries that
SP-HALs can link against. These libraries are compiled for the same
version of Android that the vendor partition is compiled against.
SP-HALs can not use libraries other than vndk-sp and ndk libs.
Membership to vndk-sp and ndk are strictly closed.

Note that in a system, there are two copies of vndk-sp libs. One at
/system/lib and the other at /vendor/lib/vndk-sp. As a result, there can
be two instances of a same library in a process.

Also adds ld.config.legacy.txt which is used on non-Treble devices where
PRODUCT_FULL_TREBLE is not set to true.
Note, this split can be cleaned up further after b/37139976 is solved.

Bug: 34407260
Test: git diff HEAD:rootdir/etc/ld.config.legacy.txt
HEAD^:rootdir/etc/ld.config.txt => 0
Test: sailfish boots (because BOARD_VNDK_VERSION is not set to
'current')

Change-Id: I8331d94edc38f22c4f8abc66cdf2050af9d0605b