Clean up includes of doublest.h and floatformat.h

Clean up includes of doublest.h and floatformat.h

As a first small step to getting rid of doublest.h, this patch removes the
include of "floatformat.h" in "doublest.h".  This is actually not needed
for the file itself.  A few source files now need to include "floatformat.h"
directly, since they got it indirectly via "doublest.h" and still need it.

In reviewing which files need it, I found a number of files that include
"floatformat.h" directly without actually needing it at all.  Similarly,
a number of files include "doublest.h" without needing it.  I've also
removed those unnecessary include statements.

gdb/ChangeLog:
2017-10-05  Ulrich Weigand  <uweigand@de.ibm.com>

	* doublest.h: Do not include "floatformat.h".  Remove stale comments.
	* gdbtypes.c: Include "floatformat.h".
	* value.c: Likewise.
	* m68k-tdep.c: Likewise.

	* findvar.c: Do not include "floatformat.h".
	* amd64-darwin-tdep.c: Likewise.
	* arm-linux-tdep.c: Likewise.
	* i386-darwin-tdep.c: Likewise.
	* i387-tdep.c: Likewise.
	* m68k-linux-tdep.c: Likewise.
	* mep-tdep.c: Likewise.
	* mips-tdep.c: Likewise.
	* nios2-tdep.c: Likewise.
	* s390-linux-tdep.c: Likewise.
	* sparc-obsd-tdep.c: Likewise.
	* sparc-tdep.c: Likewise.
	* sparc64-tdep.c: Likewise.
	* spu-tdep.c: Likewise.
	* tic6x-tdep.c: Likewise.
	* tilegx-tdep.c: Likewise.
	* vax-tdep.c: Likewise.
	* xstormy16-tdep.c: Likewise.
	* xtensa-tdep.c: Likewise.

	* top.c: Do not include "doublest.h".
	* aarch64-tdep.c: Likewise.
	* alpha-tdep.c: Likewise.
	* arm-linux-tdep.c: Likewise.
	* m68k-linux-tdep.c: Likewise.
	* tilegx-tdep.c: Likewise.
	* xstormy16-tdep.c: Likewise.