[NDS32] Remove -mgp-direct/-mno-gp-direct options.

[NDS32] Remove -mgp-direct/-mno-gp-direct options.

gcc/
	* common/config/nds32/nds32-common.c (TARGET_DEFAULT_TARGET_FLAGS):
	Remove MASK_GP_DIRECT flag.
	* config/nds32/nds32.h (MULTILIB_DEFAULTS): Have -mcmodel=medium as
	one of the multilib default options.
	* config/nds32/nds32.opt (mgp-direct): Remove.
	* config/nds32/t-mlibs (MULTILIB_OPTIONS): Use -mcmodel instead of
	-mgp-direct.  We also remove unnecessary -mlittle-endian/-mbig-endian.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@219510 138bc75d-0d04-0410-961f-82ee72b054a4