MIPS: boot/compressed/: add __bswapdi2() to target for ZSTD decompression

For MIPS pre-boot, when CONFIG_KERNEL_ZSTD=y, the decompressor
function uses __bswapdi2(), so this object file should be added to
the target object file.

Fixes these build errors:

mips-linux-ld: arch/mips/boot/compressed/decompress.o: in function `xxh64':
decompress.c:(.text+0x8be0): undefined reference to `__bswapdi2'
mips-linux-ld: decompress.c:(.text+0x8c78): undefined reference to `__bswapdi2'
mips-linux-ld: decompress.c:(.text+0x8d04): undefined reference to `__bswapdi2'
mips-linux-ld: arch/mips/boot/compressed/decompress.o:decompress.c:(.text+0xa010): more undefined references to `__bswapdi2' follow

Fixes: 0652035a ("asm-generic: unaligned: remove byteshift helpers")
Fixes: cddc40f5 ("mips: always link byteswap helpers into decompressor")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: linux-mips@vger.kernel.org
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/boot/compressed/Makefile

@@ -56,6 +56,8 @@ $(obj)/uart-ath79.c: $(srctree)/arch/mips/ath79/early_printk.c
 
 vmlinuzobjs-$(CONFIG_KERNEL_XZ) += $(obj)/ashldi3.o
 
+vmlinuzobjs-$(CONFIG_KERNEL_ZSTD) += $(obj)/bswapdi.o
+
 extra-y += ashldi3.c
 $(obj)/ashldi3.c: $(obj)/%.c: $(srctree)/lib/%.c FORCE
 	$(call if_changed,shipped)
@@ -64,6 +66,10 @@ extra-y += bswapsi.c
 $(obj)/bswapsi.c: $(obj)/%.c: $(srctree)/arch/mips/lib/%.c FORCE
 	$(call if_changed,shipped)
 
+extra-y += bswapdi.c
+$(obj)/bswapdi.c: $(obj)/%.c: $(srctree)/arch/mips/lib/%.c FORCE
+	$(call if_changed,shipped)
+
 targets := $(notdir $(vmlinuzobjs-y))
 
 targets += vmlinux.bin