arch/ppc64: Make PPC64 stages select ARCH_PPC64

Also don't define the default as this result in spurious lines in the
.config.

This also cleans up an unused Kconfig file.

In the generated config.h CPU_QEMU_POWER8 is gone as expected and
ARCH_RAMSTAGE_PPC64 moves a few lines, but the value stays the same.

Change-Id: I70b64e49e1ce07b8f30d9bbc493272bdfb3bb0bf
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/31314
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/arch/ppc64/Kconfig

@@ -1,25 +1,20 @@
 config ARCH_PPC64
 	bool
-	default n
 
 config ARCH_BOOTBLOCK_PPC64
 	bool
-	default n
 	select ARCH_PPC64
 	select BOOTBLOCK_CUSTOM
 	select C_ENVIRONMENT_BOOTBLOCK
-	select ARCH_VERSTAGE_PPC64
-	select ARCH_ROMSTAGE_PPC64
-	select ARCH_RAMSTAGE_PPC64
 
 config ARCH_VERSTAGE_PPC64
 	bool
-	default n
+	select ARCH_PPC64
 
 config ARCH_ROMSTAGE_PPC64
 	bool
-	default n
+	select ARCH_PPC64
 
 config ARCH_RAMSTAGE_PPC64
 	bool
-	default n
+	select ARCH_PPC64

src/mainboard/emulation/qemu-power8/Kconfig

@@ -22,8 +22,10 @@ config BOARD_SPECIFIC_OPTIONS
 	select CPU_QEMU_POWER8
 	select BOARD_ROMSIZE_KB_4096
 	select ARCH_BOOTBLOCK_PPC64
+	select ARCH_VERSTAGE_PPC64
+	select ARCH_ROMSTAGE_PPC64
+	select ARCH_RAMSTAGE_PPC64
 	select HAVE_UART_SPECIAL
-	select ARCH_PPC64
 	select BOOT_DEVICE_NOT_SPI_FLASH
 	select MISSING_BOARD_RESET