powerpc/32s: Disable VMAP stack which CONFIG_ADB_PMU

low_sleep_handler() can't restore the context from virtual
stack because the stack can hardly be accessed with MMU OFF.

For now, disable VMAP stack when CONFIG_ADB_PMU is selected.

Fixes: cd08f109 ("powerpc/32s: Enable CONFIG_VMAP_STACK")
Cc: stable@vger.kernel.org # v5.6+
Reported-by: Giuseppe Sacco <giuseppe@sguazz.it>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ec96c15bfa1a7415ab604ee1c98cd45779c08be0.1598553015.git.christophe.leroy@csgroup.eu

arch/powerpc/platforms/Kconfig.cputype

@@ -36,7 +36,7 @@ config PPC_BOOK3S_6xx
 	select PPC_HAVE_PMU_SUPPORT
 	select PPC_HAVE_KUEP
 	select PPC_HAVE_KUAP
-	select HAVE_ARCH_VMAP_STACK
+	select HAVE_ARCH_VMAP_STACK if !ADB_PMU
 
 config PPC_BOOK3S_601
 	bool "PowerPC 601"