Android: Fix swrast only build

Android: Fix swrast only build

A build of only swrast is broken as the Android EGL now depends on
libdrm as does GBM. While we could make EGL conditionally depend on
libdrm, we probably want to enable kms_dri winsys as well and that will
need libdrm enabled. So just always enable libdrm and simplify the
Android makefiles a bit.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Chih-Wei Huang <cwhuang@linux.org.tw>
[Emil Velikov: drop related inline comment]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>