timer: Add SPL_REGMAP dependency for Xilinx timer

Add SPL_REGMAP dependency when SPL is enabled. This can avoid compilation
issues if timer is selected but SPL_REGMAP not.

Reported-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/8f6c187e04cb3127bf5148ae2dbbdf55b25ea544.1655982509.git.michal.simek@amd.com
diff --git a/drivers/timer/Kconfig b/drivers/timer/Kconfig
index 44d1a81..6115637 100644
--- a/drivers/timer/Kconfig
+++ b/drivers/timer/Kconfig
@@ -276,6 +276,7 @@
 	bool "Xilinx timer support"
 	depends on TIMER
 	select REGMAP
+	select SPL_REGMAP if SPL
 	help
 	  Select this to enable support for the timer found on
 	  any Xilinx boards (axi timer).