drivers: nvadsp: Disable MBX empty intr at config

MBOX empty interrupt line is high by default; configuring AGIC line
in this state is undefined behaviour. Fix this by disabling the
interrupt at source and enabling it only after unmasking in AGIC.

Immediately upon unmasking one empty interrupt will be raised, which
must be ignored.

Bug 3432474

Change-Id: I03a26f061bb28b616626bb07153b0263540d7bd9
Signed-off-by: Viswanath L <viswanathl@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvidia/+/2672095
Reviewed-by: svcacv <svcacv@nvidia.com>
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
Reviewed-by: svc-mobile-cert <svc-mobile-cert@nvidia.com>
Reviewed-by: svc_kernel_abi <svc_kernel_abi@nvidia.com>
Reviewed-by: Dipesh Gandhi <dipeshg@nvidia.com>
Reviewed-by: Sharad Gupta <sharadg@nvidia.com>
GVS: Gerrit_Virtual_Submit

drivers/platform/tegra/nvadsp/dev.h

@@ -135,6 +135,7 @@ struct nvadsp_hwmb {
 	u32 hwmbox5_reg;
 	u32 hwmbox6_reg;
 	u32 hwmbox7_reg;
+	u32 empty_int_ie;
 };