reset: Add STi reset support

This patch adds a reset controller implementation for STMicroelectronics
STi family SoCs; it allows a group of related reset like controls found
in multiple system configuration registers to be represented by a single
controller device.

Driver code has been mainly extracted from kernel
drivers/reset/sti/reset-stih407.c

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/drivers/reset/Makefile b/drivers/reset/Makefile
index 5c4305c..2b96396 100644
--- a/drivers/reset/Makefile
+++ b/drivers/reset/Makefile
@@ -5,6 +5,7 @@
 obj-$(CONFIG_DM_RESET) += reset-uclass.o
 obj-$(CONFIG_SANDBOX_MBOX) += sandbox-reset.o
 obj-$(CONFIG_SANDBOX_MBOX) += sandbox-reset-test.o
+obj-$(CONFIG_STI_RESET) += sti-reset.o
 obj-$(CONFIG_TEGRA_CAR_RESET) += tegra-car-reset.o
 obj-$(CONFIG_TEGRA186_RESET) += tegra186-reset.o
 obj-$(CONFIG_RESET_UNIPHIER) += reset-uniphier.o