reset: stm32: add driver Kconfig option

Visible only if COMPILE_TEST is enabled, this allows to include the
driver in build tests.

Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Gabriel Fernandez <gabriel.fernandez@st.com>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
diff --git a/drivers/reset/Makefile b/drivers/reset/Makefile
index 61e4c64..6276f82 100644
--- a/drivers/reset/Makefile
+++ b/drivers/reset/Makefile
@@ -1,5 +1,4 @@
 obj-y += core.o
-obj-$(CONFIG_ARCH_STM32) += reset-stm32.o
 obj-$(CONFIG_ARCH_SUNXI) += reset-sunxi.o
 obj-$(CONFIG_ARCH_STI) += sti/
 obj-$(CONFIG_ARCH_HISI) += hisilicon/
@@ -11,5 +10,6 @@
 obj-$(CONFIG_RESET_OXNAS) += reset-oxnas.o
 obj-$(CONFIG_RESET_PISTACHIO) += reset-pistachio.o
 obj-$(CONFIG_RESET_SOCFPGA) += reset-socfpga.o
+obj-$(CONFIG_RESET_STM32) += reset-stm32.o
 obj-$(CONFIG_TI_SYSCON_RESET) += reset-ti-syscon.o
 obj-$(CONFIG_RESET_UNIPHIER) += reset-uniphier.o