Introduce BOARD_KERNEL_BINARIES to soong

Bug: 161563386
Test: use it

Change-Id: I8ff429a329a9aa2a8ab6c8b4501356a84a7aead6
diff --git a/android/config.go b/android/config.go
index cafc71b..4b3b78f 100644
--- a/android/config.go
+++ b/android/config.go
@@ -1271,3 +1271,7 @@
 func (c *deviceConfig) BoardUsesRecoveryAsBoot() bool {
 	return Bool(c.config.productVariables.BoardUsesRecoveryAsBoot)
 }
+
+func (c *deviceConfig) BoardKernelBinaries() []string {
+	return c.config.productVariables.BoardKernelBinaries
+}
diff --git a/android/variable.go b/android/variable.go
index 5826138..c1e1b42 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -344,6 +344,8 @@
 	InstallExtraFlattenedApexes *bool `json:",omitempty"`
 
 	BoardUsesRecoveryAsBoot *bool `json:",omitempty"`
+
+	BoardKernelBinaries []string `json:",omitempty"`
 }
 
 func boolPtr(v bool) *bool {