target/nios2: Use deposit32() to update ipending register

target/nios2: Use deposit32() to update ipending register

In nios2_cpu_set_irq(), use deposit32() rather than raw shift-and-mask
operations to set the appropriate bit in the ipending register.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20201129174022.26530-4-peter.maydell@linaro.org