arm64: support keyctl() system call in 32-bit mode

As is the case for a number of other architectures that have a 32-bit
compat mode, enable KEYS_COMPAT if both COMPAT and KEYS are enabled.
This allows AArch32 programs to use the keyctl() system call when
running on an AArch64 kernel.
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/Kconfig

@@ -1063,6 +1063,10 @@ config SYSVIPC_COMPAT
 	def_bool y
 	depends on COMPAT && SYSVIPC
 
+config KEYS_COMPAT
+	def_bool y
+	depends on COMPAT && KEYS
+
 endmenu
 
 menu "Power management options"