This patch is preparation for replacing all uses of ".head.text" or
".text.head" in the kernel with macros, so that the section name can
later be changed without having to touch a lot of the kernel.

Since some linker scripts do more complex things than referencing
HEAD_TEXT, we add a HEAD_TEXT_SECTION macro that just contains the
actual name.

I've defined HEAD_TEXT_SECTION in a new header,
include/linux/section-names.h, so that this section name only needs to
appear in one place.  I anticipate creating similar macro structures
for a number of other section names.

The long-term goal here is to be able to change the kernel's magic
section names to those that are compatible with -ffunction-sections
-fdata-sections.  This requires renaming all magic sections with names
of the form ".text.foo".
Signed-off-by: Tim Abbott <tabbott@mit.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>