gdb: rename floatformats_ia64_quad to floatformats_ieee_quad

gdb: rename floatformats_ia64_quad to floatformats_ieee_quad

It is better to rename floatformats_ia64_quad to floatformats_ieee_quad
to reflect the reality, and then we can clean up the related code.

As Tom Tromey said [1]:

  These files are maintained in gcc and then imported into the
  binutils-gdb repository, so any changes to them will have to
  be proposed there first.

the related changes have been merged into gcc master now [2], it is time
to do it for gdb.

[1] https://sourceware.org/pipermail/gdb-patches/2022-March/186569.html
[2] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b2dff6b2d9d6

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>