ARM: Name beagleboneblk back to beagle

* Pulkomandy pointed out that all Beagle hardware is
  very similar so we could likely get away with a single
  ARM target board.

build/jam/ArchitectureRules

@@ -284,7 +284,7 @@ rule KernelArchitectureSetup architecture
 
 		case arm :
 			switch $(HAIKU_BOOT_BOARD) {
-				case beagleboneblk :
+				case beagle :
 				{
 					HAIKU_BOOT_PLATFORM ?= u-boot ;
 					HAIKU_BOOT_FLOPPY_IMAGE_SIZE = 1440 ;