[POWERPC] Don't allow PMAC_APM_EMU for 64-bit

In b3028878 I switched the apm emulation
code to use the generic code but accidentally dropped the PPC32
dependency from the configuration symbol. This adds it back.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

drivers/macintosh/Kconfig

@@ -114,7 +114,7 @@ config PMAC_SMU
 config PMAC_APM_EMU
 	tristate "APM emulation"
 	select APM_EMULATION
-	depends on ADB_PMU && PM
+	depends on ADB_PMU && PM && PPC32
 
 config PMAC_MEDIABAY
 	bool "Support PowerBook hotswap media bay"