dm: timer: normalise SPL and TPL support

To fully support DM timer in SPL and TPL, we need a few things cleaned
up and normalised:
- inclusion of the uclass and drivers should be an all-or-nothing
  decision for each stage and under control of $(SPL_TPL_)TIMER
  instead of having the two-level configuration with TIMER and
  $(SPL_TPL_)TIMER_SUPPORT
- when $(SPL_TPL_)TIMER is enabled, the ARMv8 generic timer code can
  not be compiled in

This normalises configuration to $(SPL_TPL_)TIMER and moves the config
options to drivers/timer/Kconfig (and cleans up the collateral damage
to some defconfigs that had SPL_TIMER_SUPPORT enabled).

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/timer/Kconfig b/drivers/timer/Kconfig
index c666303..ac4832b 100644
--- a/drivers/timer/Kconfig
+++ b/drivers/timer/Kconfig
@@ -9,6 +9,24 @@
 	  will be used. The timer is usually a 32 bits free-running up
 	  counter. There may be no real tick, and no timer interrupt.
 
+config SPL_TIMER
+	bool "Enable driver model for timer drivers in SPL"
+	depends on TIMER && SPL
+	help
+	  Enable support for timer drivers in SPL. These can be used to get
+	  a timer value when in SPL, or perhaps for implementing a delay
+	  function. This enables the drivers in drivers/timer as part of an
+	  SPL build.
+
+config TPL_TIMER
+	bool "Enable driver model for timer drivers in TPL"
+	depends on TIMER && TPL
+	help
+	  Enable support for timer drivers in TPL. These can be used to get
+	  a timer value when in TPL, or perhaps for implementing a delay
+	  function. This enables the drivers in drivers/timer as part of an
+	  TPL build.
+
 config TIMER_EARLY
 	bool "Allow timer to be used early in U-Boot"
 	depends on TIMER