mailbox: add Tegra186 HSP driver

Tegra186's HSP module implements doorbells, mailboxes, semaphores, and
shared interrupts. This patch provides a driver for HSP, and hooks it
into the mailbox API. Currently, only doorbells are supported.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
index 9087512..9649b70 100644
--- a/drivers/mailbox/Kconfig
+++ b/drivers/mailbox/Kconfig
@@ -17,4 +17,11 @@
 	  Enable support for a test mailbox implementation, which simply echos
 	  back a modified version of any message that is sent.
 
+config TEGRA_HSP
+	bool "Enable Tegra HSP controller support"
+	depends on DM_MAILBOX && TEGRA
+	help
+	  This enables support for the NVIDIA Tegra HSP Hw module, which
+	  implements doorbells, mailboxes, semaphores, and shared interrupts.
+
 endmenu