MIPS: KVM: Limit Trap-and-Emulate to MIPS32R2 only

After tons of fixes to get Trap-and-Emulate build on Loongson64,
I've got panic on host machine when trying to run a VM.

I found that it can never work on 64bit systems. Revewing the
code, it looks like R6 can't supportrd by TE as well.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-Id: <20200710063047.154611-3-jiaxun.yang@flygoat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/mips/Kconfig

@@ -2202,6 +2202,7 @@ endchoice
 
 config KVM_GUEST
 	bool "KVM Guest Kernel"
+	depends on CPU_MIPS32_R2
 	depends on BROKEN_ON_SMP
 	help
 	  Select this option if building a guest kernel for KVM (Trap & Emulate)

arch/mips/kvm/Kconfig

@@ -37,10 +37,11 @@ choice
 
 config KVM_MIPS_TE
 	bool "Trap & Emulate"
+	depends on CPU_MIPS32_R2
 	help
 	  Use trap and emulate to virtualize 32-bit guests in user mode. This
 	  does not require any special hardware Virtualization support beyond
-	  standard MIPS32/64 r2 or later, but it does require the guest kernel
+	  standard MIPS32 r2 or later, but it does require the guest kernel
 	  to be configured with CONFIG_KVM_GUEST=y so that it resides in the
 	  user address segment.