[POWERPC] Fix Kconfig warning

Fix config warning related to select usage:

drivers/macintosh/Kconfig:117:warning: 'select' used by config symbol 'PMAC_APM_EMU' refers to undefined symbol 'SYS_SUPPORTS_APM_EMULATION'

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 56d3c0d..5eaeafd 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -118,6 +118,7 @@
 	depends on BUG
 
 config SYS_SUPPORTS_APM_EMULATION
+	default y if PMAC_APM_EMU
 	bool
 
 config DEFAULT_UIMAGE