MIPS: Allow R2 CPUs to turn off generation of 'ehb' instructions.

Some CPUs do not need ehb instructions after writing CP0 registers.
By allowing ehb generation to be overridden in
cpu-feature-overrides.h, we can save a few instructions in the TLB
handler hot paths.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
index d9a18b2..0e34faa 100644
--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -259,7 +259,8 @@
 	}
 
 	if (cpu_has_mips_r2) {
-		uasm_i_ehb(p);
+		if (cpu_has_mips_r2_exec_hazard)
+			uasm_i_ehb(p);
 		tlbw(p);
 		return;
 	}