xtensa: use pre- and postincrement FP load/store when available

xtensa: use pre- and postincrement FP load/store when available

Earlier versions of xtensa FPU used to support preincrement FP load and
store instructions (lsiu/ssiu). Recent FPU supports postincrement FP
load and store instructions only (lsip/ssip). Use configuration macro to
decide which version is available.

2014-10-14  Max Filippov  <jcmvbkbc@gmail.com>

gcc/
    * config/xtensa/xtensa.h (TARGET_HARD_FLOAT_POSTINC): new macro.
    * config/xtensa/xtensa.md (*lsiu, *ssiu): add dependency on
    !TARGET_HARD_FLOAT_POSTINC.
    (*lsip, *ssip): new instructions.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@216234 138bc75d-0d04-0410-961f-82ee72b054a4