powerpc: unify two CONFIG_POWERPC64_CPU entries in the same choice block

There are two CONFIG_POWERPC64_CPU entries in the "CPU selection"
choice block.

I guess the intent is to display a different prompt depending on
CPU_LITTLE_ENDIAN: "Generic (POWER5 and PowerPC 970 and above)" for big
endian, and "Generic (POWER8 and above)" for little endian.

I stumbled on this tricky use case, and worked around it on Kconfig with
commit 4d46b5b623e0 ("kconfig: fix infinite loop in sym_calc_choice()").
However, I doubt that supporting multiple entries with the same symbol
in a choice block is worth the complexity - this is the only such case
in the kernel tree.

This commit merges the two entries. Once this cleanup is accepted in
the powerpc subsystem, I will proceed to refactor the Kconfig parser.

Signed-off-by: Masahiro Yamada <[e-mail]>
Reviewed-by: Christophe Leroy <[e-mail]>
Acked-by: Michael Ellerman <[e-mail]>
Signed-off-by: Madhavan Srinivasan <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

arch/powerpc/platforms/Kconfig.cputype

···
 	  If unsure, select Generic.
 
 config POWERPC64_CPU
-	bool "Generic (POWER5 and PowerPC 970 and above)"
-	depends on PPC_BOOK3S_64 && !CPU_LITTLE_ENDIAN
+	bool "Generic 64 bits powerpc"
+	depends on PPC_BOOK3S_64
+	select ARCH_HAS_FAST_MULTIPLIER if CPU_LITTLE_ENDIAN
 	select PPC_64S_HASH_MMU
-
-config POWERPC64_CPU
-	bool "Generic (POWER8 and above)"
-	depends on PPC_BOOK3S_64 && CPU_LITTLE_ENDIAN
-	select ARCH_HAS_FAST_MULTIPLIER
-	select PPC_64S_HASH_MMU
-	select PPC_HAS_LBARX_LHARX
+	select PPC_HAS_LBARX_LHARX if CPU_LITTLE_ENDIAN
 
 config POWERPC_CPU
 	bool "Generic 32 bits powerpc"