spl: Ensure all SPL symbols in Kconfig have some SPL dependency

Tighten up symbol dependencies in a number of places.  Ensure that a SPL
specific option has at least a direct dependency on SPL.  In places
where it's clear that we depend on something more specific, use that
dependency instead.  This means in a very small number of places we can
drop redundant dependencies.

Reported-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index 39683fc..323c4fb 100644
--- a/drivers/i2c/muxes/Kconfig
+++ b/drivers/i2c/muxes/Kconfig
@@ -9,7 +9,7 @@
 
 config SPL_I2C_MUX
 	bool "Support I2C multiplexers on SPL"
-	depends on I2C_MUX
+	depends on SPL && I2C_MUX
 	help
 	  This enables I2C buses to be multiplexed, so that you can select
 	  one of several buses using some sort of control mechanism. The