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/lib/ecdsa/Kconfig b/lib/ecdsa/Kconfig
index a95c4ff..5c3d67d 100644
--- a/lib/ecdsa/Kconfig
+++ b/lib/ecdsa/Kconfig
@@ -17,6 +17,7 @@
 
 config SPL_ECDSA_VERIFY
 	bool "Enable ECDSA verification support in SPL"
+	depends on SPL
 	help
 	  Allow ECDSA signatures to be recognized and verified in SPL.