image: Use the correct checks for CRC32

Add a host Kconfig for CRC32. With this we can use CONFIG_IS_ENABLED(CRC32)
directly in the host build, so drop the unnecessary indirection.

Add a few more conditions to SPL_CRC32 to avoid build failures as well as
TPL_CRC32. Also update hash.c to make crc32 optional and to actually take
notice of SPL_CRC32.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
diff --git a/lib/Kconfig b/lib/Kconfig
index 64765ac..70bf8e7 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -496,6 +496,11 @@
 	  security applications, but it can be useful for providing a quick
 	  checksum of a block of data.
 
+config CRC32
+	def_bool y
+	help
+	  Enables CRC32 support in U-Boot. This is normally required.
+
 config CRC32C
 	bool