powerpc/microwatt: add POWER9_CPU, clear PPC_64S_HASH_MMU

Microwatt implements a subset of ISA v3.0 (which is equivalent to
the POWER9_CPU option). It is radix-only, so does not require hash
MMU support.

This saves 20kB compressed dtbImage and 56kB vmlinux size.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211201144153.2456614-19-npiggin@gmail.com

arch/powerpc/configs/microwatt_defconfig

@@ -15,6 +15,8 @@ CONFIG_EMBEDDED=y
 # CONFIG_COMPAT_BRK is not set
 # CONFIG_SLAB_MERGE_DEFAULT is not set
 CONFIG_PPC64=y
+CONFIG_POWER9_CPU=y
+# CONFIG_PPC_64S_HASH_MMU is not set
 # CONFIG_PPC_KUEP is not set
 # CONFIG_PPC_KUAP is not set
 CONFIG_CPU_LITTLE_ENDIAN=y
@@ -27,7 +29,6 @@ CONFIG_PPC_MICROWATT=y
 CONFIG_CPU_FREQ=y
 CONFIG_HZ_100=y
 CONFIG_PPC_4K_PAGES=y
-# CONFIG_PPC_MEM_KEYS is not set
 # CONFIG_SECCOMP is not set
 # CONFIG_MQ_IOSCHED_KYBER is not set
 # CONFIG_COREDUMP is not set

arch/powerpc/platforms/microwatt/Kconfig

@@ -5,7 +5,6 @@ config PPC_MICROWATT
 	select PPC_XICS
 	select PPC_ICS_NATIVE
 	select PPC_ICP_NATIVE
-	select PPC_HASH_MMU_NATIVE if PPC_64S_HASH_MMU
 	select PPC_UDBG_16550
 	select ARCH_RANDOM
 	help