target/mips: Fix possible MSA int overflow

target/mips: Fix possible MSA int overflow

Fix possible overflow in 1 << (DF_BITS(df) - 2) when DF_BITS(df)
is 64 by using a 64-bit integer for the shift operation.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Reported-by: Dmitriy Fedin <d.fedin@fobos-nt.ru>
Signed-off-by: Denis Rastyogin <gerben@altlinux.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-ID: <20250124122707.54264-1-gerben@altlinux.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>