security: select correct default LSM_MMAP_MIN_ADDR on arm on arm64

Binaries compiled for arm may run on arm64 if CONFIG_COMPAT is
selected.  Set LSM_MMAP_MIN_ADDR to 32768 if ARM64 && COMPAT to
prevent selinux failures launching 32-bit static executables that
are mapped at 0x8000.

Signed-off-by: Colin Cross <ccross@android.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Eric Paris <eparis@redhat.com>
Acked-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

security/Kconfig

@@ -103,7 +103,7 @@ config INTEL_TXT
 config LSM_MMAP_MIN_ADDR
 	int "Low address space for LSM to protect from user allocation"
 	depends on SECURITY && SECURITY_SELINUX
-	default 32768 if ARM
+	default 32768 if ARM || (ARM64 && COMPAT)
 	default 65536
 	help
 	  This is the portion of low virtual memory which should be protected