system.prop: set debug.egl.recordable.rgba8888

From mako:
With the last Adreno GL libraries, the EGL_ANDROID_recordable extension is not
configured for RGBA8888. Subsequently, SurfaceFlinger is not guaranteed to
select a config that supports either EGL_ANDROID_recordable or
EGL_ANDROID_framebuffer_target, as can be seen from these errors at boot.

W/SurfaceFlinger(  160): no suitable EGLConfig found, trying without EGL_FRAMEBUFFER_TARGET_ANDROID
W/SurfaceFlinger(  160): no suitable EGLConfig found, trying without EGL_RECORDABLE_ANDROID

This is due to a missing property setting for debug.egl.recordable.rgba8888,
which is set by this patch.

Bug: 7191369
Change-Id: Icbf56c0b991c0242739207074d23333d6b0975ef
Signed-off-by: Iliyan Malchev <malchev@google.com>
jenad: clean-up system.prop, update readme
readme