arm64: Kconfig: select COMPAT_BINFMT_ELF only when BINFMT_ELF is set

Fix warning:
"(COMPAT) selects COMPAT_BINFMT_ELF which has unmet direct dependencies
(COMPAT && BINFMT_ELF)"
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/Kconfig

@@ -1011,7 +1011,7 @@ source "fs/Kconfig.binfmt"
 config COMPAT
 	bool "Kernel support for 32-bit EL0"
 	depends on ARM64_4K_PAGES || EXPERT
-	select COMPAT_BINFMT_ELF
+	select COMPAT_BINFMT_ELF if BINFMT_ELF
 	select HAVE_UID16
 	select OLD_SIGSUSPEND3
 	select COMPAT_OLD_SIGACTION