powerpc/prom: convert PROM_BUG() to standard trap

Prior to commit 1bd98d7fbaf5 ("ppc64: Update BUG handling based on
ppc32"), BUG() family was using BUG_ILLEGAL_INSTRUCTION which
was an invalid instruction opcode to trap into program check
exception.

That commit converted them to using standard trap instructions,
but prom/prom_init and their PROM_BUG() macro were left over.
head_64.S and exception-64s.S were left aside as well.

Convert them to using the standard BUG infrastructure.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/cdaf4bbbb64c288a077845846f04b12683f8875a.1566817807.git.christophe.leroy@c-s.fr

arch/powerpc/include/asm/bug.h

@@ -5,14 +5,6 @@
 
 #include <asm/asm-compat.h>
 
-/*
- * Define an illegal instr to trap on the bug.
- * We don't use 0 because that marks the end of a function
- * in the ELF ABI.  That's "Boo Boo" in case you wonder...
- */
-#define BUG_OPCODE .long 0x00b00b00  /* For asm */
-#define BUG_ILLEGAL_INSTR "0x00b00b00" /* For BUG macro */
-
 #ifdef CONFIG_BUG
 
 #ifdef __ASSEMBLY__

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

@@ -1467,7 +1467,8 @@ EXC_COMMON_BEGIN(fp_unavailable_common)
 	RECONCILE_IRQ_STATE(r10, r11)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	kernel_fp_unavailable_exception
-	BUG_OPCODE
+0:	trap
+	EMIT_BUG_ENTRY 0b, __FILE__, __LINE__, 0
 1:
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 BEGIN_FTR_SECTION

arch/powerpc/kernel/head_64.S

@@ -182,7 +182,8 @@ __secondary_hold:
 	isync
 	bctr
 #else
-	BUG_OPCODE
+0:	trap
+	EMIT_BUG_ENTRY 0b, __FILE__, __LINE__, 0
 #endif
 CLOSE_FIXED_SECTION(first_256B)
 
@@ -998,7 +999,8 @@ start_here_common:
 	bl	start_kernel
 
 	/* Not reached */
-	BUG_OPCODE
+	trap
+	EMIT_BUG_ENTRY 0b, __FILE__, __LINE__, 0
 
 /*
  * We put a few things here that have to be page-aligned.

arch/powerpc/kernel/prom_init.c

@@ -94,7 +94,7 @@ static int of_workarounds __prombss;
 #define PROM_BUG() do {						\
         prom_printf("kernel BUG at %s line 0x%x!\n",		\
 		    __FILE__, __LINE__);			\
-        __asm__ __volatile__(".long " BUG_ILLEGAL_INSTR);	\
+	__builtin_trap();					\
 } while (0)
 
 #ifdef DEBUG_PROM