MIPS: Compat: Fix build error if CONFIG_MIPS32_COMPAT but no compat ABI.

In that case nor __NR_seccomp_*_32 symbols will be defined in
<asm/unistd.h> so the attempt to use it in kernel.seccomp.c will fail
with:

kernel/seccomp.c:565:2: error: '__NR_seccomp_read_32' undeclared here (not in a function)
  __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
  ^
kernel/seccomp.c:565:24: error: '__NR_seccomp_write_32' undeclared here (not in a function)
  __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
                        ^
kernel/seccomp.c:565:47: error: '__NR_seccomp_exit_32' undeclared here (not in a function)
  __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
                                               ^
kernel/seccomp.c:565:69: error: '__NR_seccomp_sigreturn_32' undeclared here (not in a function)
  __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,

Solved by changing the compat ABIs in kconfig to select MIPS32_COMPAT
directly.  This also means the user no longer has to select MIPS32_COMPAT
before being able to see the ABI options.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -2656,27 +2656,21 @@ config TRAD_SIGNALS
 	bool
 
 config MIPS32_COMPAT
-	bool "Kernel support for Linux/MIPS 32-bit binary compatibility"
-	depends on 64BIT
-	help
-	  Select this option if you want Linux/MIPS 32-bit binary
-	  compatibility. Since all software available for Linux/MIPS is
-	  currently 32-bit you should say Y here.
+	bool
 
 config COMPAT
 	bool
-	depends on MIPS32_COMPAT
-	select ARCH_WANT_OLD_COMPAT_IPC
-	default y
 
 config SYSVIPC_COMPAT
 	bool
-	depends on COMPAT && SYSVIPC
-	default y
 
 config MIPS32_O32
 	bool "Kernel support for o32 binaries"
-	depends on MIPS32_COMPAT
+	depends on 64BIT
+	select ARCH_WANT_OLD_COMPAT_IPC
+	select COMPAT
+	select MIPS32_COMPAT
+	select SYSVIPC_COMPAT if SYSVIPC
 	help
 	  Select this option if you want to run o32 binaries.  These are pure
 	  32-bit binaries as used by the 32-bit Linux/MIPS port.  Most of
@@ -2687,6 +2681,9 @@ config MIPS32_O32
 config MIPS32_N32
 	bool "Kernel support for n32 binaries"
 	depends on MIPS32_COMPAT
+	select COMPAT
+	select MIPS32_COMPAT
+	select SYSVIPC_COMPAT if SYSVIPC
 	help
 	  Select this option if you want to run n32 binaries.  These are
 	  64-bit binaries using 32-bit quantities for addressing and certain