powerpc/rtas: Remove machine_check_in_rtas()

machine_check_in_rtas() is just a trap.

Do the trap directly in the machine check exception handler.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/78899f40f89cb3c4f69bdff7f04eb6ec7cb753d5.1585670437.git.christophe.leroy@c-s.fr

arch/powerpc/kernel/entry_32.S

@@ -1380,10 +1380,4 @@ _GLOBAL(enter_rtas)
 	mtspr	SPRN_SRR0,r8
 	mtspr	SPRN_SRR1,r9
 	RFI			/* return to caller */
-
-	.globl	machine_check_in_rtas
-machine_check_in_rtas:
-	twi	31,0,0
-	/* XXX load up BATs and panic */
-
 #endif /* CONFIG_PPC_RTAS */

arch/powerpc/kernel/head_32.S

@@ -297,7 +297,7 @@ MachineCheck:
 	cmpwi	cr1, r4, 0
 #endif
 	beq	cr1, machine_check_tramp
-	b	machine_check_in_rtas
+	twi	31, 0, 0
 #else
 	b	machine_check_tramp
 #endif