ARM: Simplify board specification

* Don't assume verdex as it isn't clear this was
  occurring.
* Make an educated guess on HAIKU_BOOT_PLATFORM
  based on provided board (but still allow it to
  be overridden)
* Error out if user doesn't populate
  HAIKU_BOOT_PLATFORM or enters an unknown board
  name.
* You need to add "-sHAIKU_BOOT_BOARD=xxx" to
  your jam to build for the proper ARM device.
* Rename beagle to beagleboneblk as per the
  documentation.

build/jam/ArchitectureRules

@@ -283,10 +283,39 @@ rule KernelArchitectureSetup architecture
 			HAIKU_BOOT_ARCHIVE_IMAGE_OFFSET = 192 ; # in kB - unused yet
 
 		case arm :
-			HAIKU_BOOT_PLATFORM ?= u-boot ;
-			HAIKU_BOOT_BOARD ?= verdex ;
-			HAIKU_BOOT_FLOPPY_IMAGE_SIZE = 1440 ;
-				# in kB (there is not really a floppy on the gumstix ;) )
+			switch $(HAIKU_BOOT_BOARD) {
+				case beagleboneblk :
+				{
+					HAIKU_BOOT_PLATFORM ?= u-boot ;
+					HAIKU_BOOT_FLOPPY_IMAGE_SIZE = 1440 ;
+				}
+				case neo_freerunner :
+				{
+					HAIKU_BOOT_PLATFORM ?= u-boot ;
+					HAIKU_BOOT_FLOPPY_IMAGE_SIZE = 1440 ;
+				}
+				case overo :
+				{
+					HAIKU_BOOT_PLATFORM ?= u-boot ;
+					HAIKU_BOOT_FLOPPY_IMAGE_SIZE = 1440 ;
+				}
+				case raspberry_pi :
+				{
+					# For now rpi has a custom non u-boot loader
+					HAIKU_BOOT_PLATFORM ?= raspberrypi_arm ;
+					HAIKU_BOOT_FLOPPY_IMAGE_SIZE = 1440 ;
+				}
+				case verdex :
+				{
+					HAIKU_BOOT_PLATFORM ?= u-boot ;
+					HAIKU_BOOT_FLOPPY_IMAGE_SIZE = 1440 ;
+				}
+				case * :
+				{
+					Exit "Set HAIKU_BOOT_BOARD for your target ARM device!" ;
+				}
+			}
+					
 			# offset in floppy image (>= sizeof(haiku_loader))
 			HAIKU_BOOT_ARCHIVE_IMAGE_OFFSET = 192 ; # in kB - unused yet