target/mips: Fix emulation of nanoMIPS MTHLIP instruction

target/mips: Fix emulation of nanoMIPS MTHLIP instruction

The field ac in nanoMIPS instruction MTHLIP rs, ac is specified in
nanoMIPS documentation as opcode[15..14] (2 bits). However, in the
current QEMU code, the corresponding argument passed to the helper
gen_helper_mthlip() has the value of opcode[15..11] (5 bits). Right
shift the value of this argument by three bits to fix this.

Signed-off-by: Stefan Pejic <stefan.pejic@syrmia.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220504110403.613168-2-stefan.pejic@syrmia.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>