powerpc/64: Make ELFv2 the default for big-endian builds

All supported toolchains now support ELFv2 on big-endian, so flip the
default on this and hide the option behind EXPERT for the purpose of
bug hunting.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230606093832.199712-3-npiggin@gmail.com

arch/powerpc/Kconfig

@@ -624,8 +624,10 @@ config ARCH_HAS_KEXEC_PURGATORY
 	def_bool KEXEC_FILE
 
 config PPC64_BIG_ENDIAN_ELF_ABI_V2
-	prompt "Build big-endian kernel using ELF ABI V2 (EXPERIMENTAL)" if LD_IS_BFD
-	def_bool y if LD_IS_LLD
+	# Option is available to BFD, but LLD does not support ELFv1 so this is
+	# always true there.
+	prompt "Build big-endian kernel using ELF ABI V2" if LD_IS_BFD && EXPERT
+	def_bool y
 	depends on PPC64 && CPU_BIG_ENDIAN
 	depends on CC_HAS_ELFV2
 	help