util: Put qemu_vfree() in memalign.c

util: Put qemu_vfree() in memalign.c

qemu_vfree() is the companion free function to qemu_memalign(); put
it in memalign.c so the allocation and free functions are together.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220226180723.1706285-9-peter.maydell@linaro.org
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>