Change "Foo& foo" declarations to "Foo &foo".

Change "Foo& foo" declarations to "Foo &foo".
This primarily to be internally consistent (sometimes we used one,
sometimes the other, even within the same line of code!).
I picked the latter to be symmetric with "Foo *foo".

base/cprintf_formats.hh:
base/range.hh:
base/refcnt.hh:
base/res_list.hh:
base/statistics.hh:
base/str.hh:
cpu/exec_context.hh:
cpu/simple_cpu/simple_cpu.cc:
cpu/simple_cpu/simple_cpu.hh:
sim/serialize.cc:
sim/serialize.hh:
sim/syscall_emul.hh:
    Change "Foo& foo" declarations to "Foo &foo".

--HG--
extra : convert_revision : ca1b0e85a578b539214bda3b8d61ac23792f2e87