mailbox: qcom: Add QCS404 APPS Global compatible

Add support for the QCS404 APPS Global block with IPC register at offset
8.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>