powerpc: Change CONFIG_E500 to CONFIG_PPC_E500

It will be used outside arch/powerpc, make it clear its a
powerpc configuration item.

And we already have CONFIG_PPC_E500MC, so that will make
it more consistent.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e63b22083c11c4300f4a82d3123a46e5fdd54fa6.1663606876.git.christophe.leroy@csgroup.eu

arch/powerpc/sysdev/fsl_pci.c

@@ -943,7 +943,7 @@ u64 fsl_pci_immrbar_base(struct pci_controller *hose)
 	return 0;
 }
 
-#ifdef CONFIG_E500
+#ifdef CONFIG_PPC_E500
 static int mcheck_handle_load(struct pt_regs *regs, u32 inst)
 {
 	unsigned int rd, ra, rb, d;

arch/powerpc/sysdev/fsl_rio.c

@@ -98,7 +98,7 @@ resource_size_t rio_law_start;
 struct fsl_rio_dbell *dbell;
 struct fsl_rio_pw *pw;
 
-#ifdef CONFIG_E500
+#ifdef CONFIG_PPC_E500
 int fsl_rio_mcheck_exception(struct pt_regs *regs)
 {
 	const struct exception_table_entry *entry;