crypto: move crypto objects out of libqemuutil.la

Future patches will be adding more crypto related APIs which
rely on QOM infrastructure. This creates a problem, because
QOM relies on library constructors to register objects. When
you have a file in a static .a library though which is only
referenced by a constructor the linker is dumb and will drop
that file when linking to the final executable :-( The only
workaround for this is to link the .a library to the executable
using the -Wl,--whole-archive flag, but this creates its own
set of problems because QEMU is relying on lazy linking for
libqemuutil.a. Using --whole-archive majorly increases the
size of final executables as they now contain a bunch of
object code they don't actually use.

The least bad option is to thus not include the crypto objects
in libqemuutil.la, and instead define a crypto-obj-y variable
that is referenced directly by all the executables that need
this code (tools + softmmu, but not qemu-ga). We avoid pulling
entire of crypto-obj-y into the userspace emulators as that
would force them to link to gnutls too, which is not required.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

crypto/Makefile.objs

@@ -1,5 +1,8 @@
-util-obj-y += init.o
-util-obj-y += hash.o
-util-obj-y += aes.o
-util-obj-y += desrfb.o
-util-obj-y += cipher.o
+crypto-obj-y = init.o
+crypto-obj-y += hash.o
+crypto-obj-y += aes.o
+crypto-obj-y += desrfb.o
+crypto-obj-y += cipher.o
+
+# Let the userspace emulators avoid linking gnutls/etc
+crypto-aes-obj-y = aes.o