sparc64: Fix sun4u execute bit check in TSB I-TLB load.

Thanks to testcase and report from Brad Spengler:

--------------------
#include <stdio.h>

typedef int (* _wee)(void);

int main(void)
{
        char buf[8] = { '\x81', '\xc7', '\xe0', '\x08', '\x81', '\xe8',
                        '\x00', '\x00' };
        _wee wee;
        printf("%p\n", &buf);
        wee = (_wee)&buf;
        wee();

        return 0;
}
--------------------

TSB I-tlb load code tries to use andcc to check the _PAGE_EXEC_4U bit,
but that's bit 12 so it gets sign extended all the way up to bit 63
and the test nearly always passes as a result.

Use sethi to fix the bug.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc/kernel/tsb.S

@@ -191,10 +191,12 @@ tsb_dtlb_load:
 
 tsb_itlb_load:
 	/* Executable bit must be set.  */
-661:	andcc		%g5, _PAGE_EXEC_4U, %g0
-	.section	.sun4v_1insn_patch, "ax"
+661:	sethi		%hi(_PAGE_EXEC_4U), %g4
+	andcc		%g5, %g4, %g0
+	.section	.sun4v_2insn_patch, "ax"
 	.word		661b
 	andcc		%g5, _PAGE_EXEC_4V, %g0
+	nop
 	.previous
 
 	be,pn		%xcc, tsb_do_fault