target/sh4: Honor QEMU_LOG_FILENAME with QEMU_LOG=cpu

When using QEMU_LOG=cpu on sh4, QEMU_LOG_FILENAME is partially ignored.
Fix by using qemu_fprintf() instead of qemu_printf() in the respective
places.

Fixes: 90c84c56 ("qom/cpu: Simplify how CPUClass:cpu_dump_state() prints")
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230316003411.129462-1-iii@linux.ibm.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>