Disable MIPS64 ISAs for MIPS32 targets

Currently you can select MIPS64 ISAs, like mips64 and mips64r2, for
MIPS32 targets. This is incorrect, so we disable the possibility to do
that.

Reviewed-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: Vicente Olivert Riera <vincent.riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

arch/Config.in.mips

@@ -29,8 +29,10 @@ config BR2_mips_32r2
 	depends on !BR2_ARCH_IS_64
 config BR2_mips_64
 	bool "mips 64"
+	depends on BR2_ARCH_IS_64
 config BR2_mips_64r2
 	bool "mips 64r2"
+	depends on BR2_ARCH_IS_64
 endchoice