Loongarch: Fix plugin header missing install.

gcc/ChangeLog:

	* config/loongarch/t-loongarch: Add loongarch-driver.h into
	TM_H. Add loongarch-def.h and loongarch-tune.h into
	OPTIONS_H_EXTRA.

Co-authored-by: Lulu Cheng <chenglulu@loongson.cn>

gcc/config/loongarch/t-loongarch

@@ -16,6 +16,10 @@
 # along with GCC; see the file COPYING3.  If not see
 # <http://www.gnu.org/licenses/>.
 
+TM_H += $(srcdir)/config/loongarch/loongarch-driver.h
+OPTIONS_H_EXTRA += $(srcdir)/config/loongarch/loongarch-def.h \
+		   $(srcdir)/config/loongarch/loongarch-tune.h
+
 # Canonical target triplet from config.gcc
 LA_MULTIARCH_TRIPLET = $(patsubst LA_MULTIARCH_TRIPLET=%,%,$\
 $(filter LA_MULTIARCH_TRIPLET=%,$(tm_defines)))