powerpc: Fix HMIs on big-endian with CONFIG_RELOCATABLE=y

[ Upstream commit 505a314f ]

HMIs will crash the kernel due to

	BRANCH_LINK_TO_FAR(hmi_exception_realmode)

Calling into the OPD instead of the actual code.

Fixes: 2337d207 ("powerpc/64: CONFIG_RELOCATABLE support for hmi interrupts")
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[mpe: Use DOTSYM() rather than #ifdef]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/powerpc/kernel/exceptions-64s.S

@@ -1123,7 +1123,7 @@ TRAMP_REAL_BEGIN(hmi_exception_early)
 	EXCEPTION_PROLOG_COMMON_2(PACA_EXGEN)
 	EXCEPTION_PROLOG_COMMON_3(0xe60)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	BRANCH_LINK_TO_FAR(hmi_exception_realmode) /* Function call ABI */
+	BRANCH_LINK_TO_FAR(DOTSYM(hmi_exception_realmode)) /* Function call ABI */
 	cmpdi	cr0,r3,0
 
 	/* Windup the stack. */