RISC-V: Build tishift only on 64-bit

Only RV64 supports 128 integer size.
Signed-off-by: Zong Li <zong@andestech.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/lib/Makefile

@@ -2,6 +2,7 @@ lib-y	+= delay.o
 lib-y	+= memcpy.o
 lib-y	+= memset.o
 lib-y	+= uaccess.o
-lib-y	+= tishift.o
+
+lib-(CONFIG_64BIT) += tishift.o
 
 lib-$(CONFIG_32BIT) += udivdi3.o