core_kernel_data(): Fix architectures that do not define _sdata

core_kernel_data(): Fix architectures that do not define _sdata

Some architectures such as Alpha do not define _sdata but _data:

  kernel/built-in.o: In function `core_kernel_data':
  kernel/extable.c:77: undefined reference to `_sdata'

So expand the scope of the data range to the text addresses too,
this might be more correct anyway because this way we can
cover readonly variables as well.

Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/n/tip-i878c8a0e0g0ep4v7i6vxnhz@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>