selftests: vm: Makefile: rename TARGETS to VMTARGETS

The tools/testing/selftests/vm/Makefile uses the variable TARGETS
internally to generate a list of platform-specific binary build targets
suffixed with _{32,64}.  When building the selftests using its own
Makefile directly, such as via the following command run in a kernel tree:

One receives an error such as the following:

make: Entering directory '/root/linux/tools/testing/selftests'
make --no-builtin-rules ARCH=x86 -C ../../.. headers_install
make[1]: Entering directory '/root/linux'
  INSTALL ./usr/include
make[1]: Leaving directory '/root/linux'
make[1]: Entering directory '/root/linux/tools/testing/selftests/vm'
make[1]: *** No rule to make target 'vm.c', needed by '/root/linux/tools/testing/selftests/vm/vm_64'.  Stop.
make[1]: Leaving directory '/root/linux/tools/testing/selftests/vm'
make: *** [Makefile:175: all] Error 2
make: Leaving directory '/root/linux/tools/testing/selftests'

The TARGETS variable passed to tools/testing/selftests/Makefile collides
with the TARGETS used in tools/testing/selftests/vm/Makefile, so rename
the latter to VMTARGETS, eliminating the collision with no functional
change.

Link: https://lkml.kernel.org/r/20220504213454.1282532-1-jsavitz@redhat.com
Fixes: f21fda8f

 ("selftests: vm: pkeys: fix multilib builds for x86")
Signed-off-by: Joel Savitz <jsavitz@redhat.com>
Acked-by: Nico Pache <npache@redhat.com>
Cc: Joel Savitz <jsavitz@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Sandipan Das <sandipan@linux.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>