powerpc/64: Make VDSO32 track COMPAT on 64-bit

When we added the VDSO32 kconfig symbol, which controls building of
the 32-bit VDSO, we made it depend on CPU_BIG_ENDIAN (for 64-bit).

That was because back then COMPAT was always enabled for 64-bit, so
depending on it would have left the 32-bit VDSO always enabled, which
we didn't want.

But since then we have made COMPAT selectable, and off by default for
ppc64le, so VDSO32 should really depend on that.

For most people this makes no difference, none of the defconfigs
change, it's only if someone is building ppc64le with COMPAT=y, they
will now also get VDSO32. If they've enabled COMPAT in order to run
32-bit binaries they presumably also want the 32-bit VDSO.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20200908125850.407939-1-mpe@ellerman.id.au

arch/powerpc/platforms/Kconfig.cputype

@@ -490,13 +490,12 @@ endmenu
 
 config VDSO32
 	def_bool y
-	depends on PPC32 || CPU_BIG_ENDIAN
+	depends on PPC32 || COMPAT
 	help
 	  This symbol controls whether we build the 32-bit VDSO. We obviously
 	  want to do that if we're building a 32-bit kernel. If we're building
-	  a 64-bit kernel then we only want a 32-bit VDSO if we're building for
-	  big endian. That is because the only little endian configuration we
-	  support is ppc64le which is 64-bit only.
+	  a 64-bit kernel then we only want a 32-bit VDSO if we're also enabling
+	  COMPAT.
 
 choice
 	prompt "Endianness selection"