rng: stm32: rename STM32 RNG driver

Rename the RNG driver as it is usable by other STM32 platforms
than the STM32MP1x ones. Rename CONFIG_RNG_STM32MP1 to
CONFIG_RNG_STM32

Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Reviewed-by: Grzegorz Szymaszek <gszymaszek@short.pl>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 1999191..db4279a 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -621,7 +621,7 @@
 F:	drivers/remoteproc/stm32_copro.c
 F:	drivers/reset/stm32-reset.c
 F:	drivers/rng/optee_rng.c
-F:	drivers/rng/stm32mp1_rng.c
+F:	drivers/rng/stm32_rng.c
 F:	drivers/rtc/stm32_rtc.c
 F:	drivers/serial/serial_stm32.*
 F:	drivers/spi/stm32_qspi.c