rpi: Add new beta loader

* Sets uart up for us
* Enhanced non-linux os loading
* Supports device trees
* Add config.txt example with sample settings

build/jam/board/raspberry_pi/config.txt

@@ -0,0 +1,38 @@
+##### Overclocking
+# WARNING: Don't adjust unless you know what you are doing!
+#arm_freq=800
+#gpu_freq=350
+#core_freq=250
+#h264_freq=250
+#isp_freq=250
+#v3d_freq=250
+#sdram_freq=250
+#over_voltage=0
+#over_voltage_sdram=0
+#over_voltage_sdram_c=0
+#over_voltage_sdram_i=0
+#over_voltage_sdram_p=0
+
+
+##### Video
+#sdtv_mode=0
+#sdtv_aspect=1
+#hdmi_mode=19
+#hdmi_drive=
+#test_mode=0
+#disable_overscan=0
+enable_l2cache=1
+
+
+##### Low level
+# Skip boot tags for non-linux platforms
+disable_commandline_tags=1
+#kernel_address=
+#device_tree=bcm2835.dtb
+#device_tree_address=0x100
+
+
+##### UART Settings
+# Default is 115200
+#init_uart_baud=9600
+#init_uart_clock=

build/jam/board/raspberry_pi/info.txt

@@ -11,6 +11,7 @@ get them from one of the official images:
 * bootcode.bin : 2nd stage bootloader, starts with SDRAM disabled
 * loader.bin : 3rd stage bootloader, starts with SDRAM enabled
 * start.elf: The GPU binary firmware image, provided by the foundation.
+  * For now, use beta_start.elf
 * kernel.img: The OS kernel to load on the ARM processor.
   Normally this is Linux - see instructions for compiling a kernel.
 * cmdline.txt: Parameters passed to the kernel on boot.