Introduce BOARD_KERNEL_BINARIES to soong

Bug: 161563386
Test: use it

Change-Id: I8ff429a329a9aa2a8ab6c8b4501356a84a7aead6

android/config.go

@@ -1271,3 +1271,7 @@ func (c *deviceConfig) DeviceSecondaryArchVariant() string {
 func (c *deviceConfig) BoardUsesRecoveryAsBoot() bool {
 	return Bool(c.config.productVariables.BoardUsesRecoveryAsBoot)
 }
+
+func (c *deviceConfig) BoardKernelBinaries() []string {
+	return c.config.productVariables.BoardKernelBinaries
+}

android/variable.go

@@ -344,6 +344,8 @@ type productVariables struct {
 	InstallExtraFlattenedApexes *bool `json:",omitempty"`
 
 	BoardUsesRecoveryAsBoot *bool `json:",omitempty"`
+
+	BoardKernelBinaries []string `json:",omitempty"`
 }
 
 func boolPtr(v bool) *bool {