powerpc/boot: Specify ABI v2 when building an LE boot wrapper

commit 655471f5 upstream.

The kernel does it, not the boot wrapper, which breaks with some
cross compilers that still default to ABI v1.

Fixes: 147c0516 ("powerpc/boot: Add support for 64bit little endian wrapper")
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

arch/powerpc/boot/Makefile

@@ -28,6 +28,9 @@ BOOTCFLAGS	+= -m64
 endif
 ifdef CONFIG_CPU_BIG_ENDIAN
 BOOTCFLAGS	+= -mbig-endian
+else
+BOOTCFLAGS	+= -mlittle-endian
+BOOTCFLAGS	+= $(call cc-option,-mabi=elfv2)
 endif
 
 BOOTAFLAGS	:= -D__ASSEMBLY__ $(BOOTCFLAGS) -traditional -nostdinc