clear-once: Add missing dependency on u-boot

This script depends on u-boot-fw-utils so add it as a runtime
dependency.

Additionally allow u-boot-fw-utils to be provided by alternate
recipes.

Tested: Verified palmetto, qemu and witherspoon images build
Change-Id: I7b0492d9237efa6e449d63b106320273bed63c98
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-phosphor/common/recipes-phosphor/clear-once/clear-once.bb b/meta-phosphor/common/recipes-phosphor/clear-once/clear-once.bb
index 89b83ce..79a7ecd 100644
--- a/meta-phosphor/common/recipes-phosphor/clear-once/clear-once.bb
+++ b/meta-phosphor/common/recipes-phosphor/clear-once/clear-once.bb
@@ -1,5 +1,7 @@
 SUMMARY = "Clear boot-once variables"
 DESCRIPTION = "Clear u-boot variables used for one-time boot flow"
 
+RDEPENDS_${PN} = "${@d.getVar('PREFERRED_PROVIDER_u-boot-fw-utils', True) or 'u-boot-fw-utils'}"
+
 inherit obmc-phosphor-systemd
 inherit obmc-phosphor-license