ARM: omap3: beagle: Enable DM_SERIAL, update distro usage and NAND layout

ARM: omap3: beagle: Enable DM_SERIAL, update distro usage and NAND layout

This commit does the following for BeagleBoard{-xM}:

- Enable DM_SERIAL which also enables SPL_DM_SERIAL
- Misc. config updates in support of DM_SERIAL
- Use updated NAND layout (BeagleBoard):

	device nand0 <omap2-nand.0>, # parts = 6

	#: name		size			offset
	-------------------------------------------------
	0: spl		0x00080000(512k)	0x00000000
	1: u-boot	0x001e0000(1920k)	0x00080000
	2: u-boot-env	0x00020000(128k)	0x00260000
	3: dtb		0x00020000(128k)	0x00280000
	4: kernel	0x00600000(6m)		0x002a0000
	5: rootfs	0x0f760000(-)		0x008a0000
	-------------------------------------------------

- Use MMC and UBIFS support from config_distro_bootcmd.h
- Use LEGACY_MMC and NAND support defined in omap3_beagle.h

[MMC(0:1)/extlinux/extlinux.conf]
---8<-------------------------------------------------------------------
default omap3-beagle-mmc-fat
label omap3-beagle-mmc-fat
	kernel /zImage
	fdt /omap3-beagle.dtb
	append console=ttyO2,115200n8 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait
---8<-------------------------------------------------------------------

[LEGACY_MMC(0:2)/boot/extlinux/extlinux.conf]
---8<-------------------------------------------------------------------
default omap3-beagle-mmc-ext4
label omap3-beagle-mmc-ext4
	kernel /boot/zImage
	fdt /boot/omap3-beagle.dtb
	append console=ttyO2,115200n8 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait
---8<-------------------------------------------------------------------

[UBIFS(ubi0:rootfs)/boot/extlinux/extlinux.conf]
---8<-------------------------------------------------------------------
default omap3-beagle-nand-ubifs
label omap3-beagle-nand-ubifs
	kernel /boot/zImage
	fdt /boot/omap3-beagle.dtb
	append console=ttyO2,115200n8 root=ubi0:rootfs rw ubi.mtd=rootfs rootfstype=ubifs rootwait
---8<-------------------------------------------------------------------

The board's 'bootcmd' can also be overridden with:

	CONFIG_BOOTCOMMAND="run findfdt; run mmcboot"
	CONFIG_BOOTCOMMAND="run findfdt; run nandboot"
	CONFIG_BOOTCOMMAND="run findfdt; run ramboot"

		or

	CONFIG_BOOTCOMMAND="run findfdt; run somethingelse"

The use of 'run findfdt' is required.

Signed-off-by: Derald D. Woods <woods.technical@gmail.com>