powerpc: Don't flush/invalidate the d/icache for an unknown relocation type

For an unknown relocation type since the value of r4 is just the 8bit
relocation type, the sum of r4 and r7 may yield an invalid memory
address. For example:
In normal case:
r4 = c00xxxxx
r7 = 40000000
r4 + r7 = 000xxxxx

For an unknown relocation type:
r4 = 000000xx
r7 = 40000000
r4 + r7 = 400000xx
400000xx is an invalid memory address for a board which has just
512M memory.

And for operations such as dcbst or icbi may cause bus error for an
invalid memory address on some platforms and then cause the board
reset. So we should skip the flush/invalidate the d/icache for
an unknown relocation type.

Signed-off-by: Kevin Hao <[e-mail]>
Acked-by: Suzuki K. Poulose <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/kernel/reloc_32.S

···
 	/* R_PPC_ADDR16_LO */
 lo16:
 	cmpwi	r4, R_PPC_ADDR16_LO
-	bne	nxtrela
+	bne	unknown_type
 	lwz	r4, 0(r9)	/* r_offset */
 	lwz	r0, 8(r9)	/* r_addend */
 	add	r0, r0, r3
···
 	dcbst	r4,r7
 	sync			/* Ensure the data is flushed before icbi */
 	icbi	r4,r7
+unknown_type:
 	cmpwi	r8, 0		/* relasz = 0 ? */
 	ble	done
 	add	r9, r9, r6	/* move to next entry in the .rela table */