ARM: omap3: evm: Fix 'fitImage' booting

This commit sets two additional variables in the default BOOTCOMMAND.
Adding 'boot=mmc' and 'addr_fit=0x8b000000' removes the need for a
special 'uEnv.txt' to be created. The 'addr_fit' variable is the key
piece here. It is normally defined as 0x90000000, in the macro
DEFAULT_FIT_TI_ARGS. For this OMAP34XX board, 0x8b000000 works without
touching other varibles. This was tested with a 'fitImage' created
using the following FIT source:

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/dts-v1/;

/ {
	description = "Simple image with single Linux kernel and FDT blob";
	#address-cells = <1>;

	images {
		kernel {
			description = "Linux kernel: omap2plus";
			data = /incbin/("./zImage");
			type = "kernel";
			arch = "arm";
			os = "linux";
			compression = "none";
			load = <0x80008000>;
			entry = <0x80008000>;
			hash-1 {
				algo = "sha256";
			};
		};
		fdt-omap3-evm.dtb {
			description = "FDT: omap3-evm.dtb";
			data = /incbin/("./omap3-evm.dtb");
			type = "flat_dt";
			arch = "arm";
			compression = "none";
			load = <0x8ff00000>;
			hash-1 {
				algo = "sha256";
			};
		};
	};

	configurations {
		default = "conf-omap3-evm.dtb";
		conf-omap3-evm.dtb {
			description = "Boot Linux kernel with FDT blob";
			kernel = "kernel";
			fdt = "fdt-omap3-evm.dtb";
		};
	};
};
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Additionally, the default environment is now stored in "uboot.env" on
the FAT partition of MMC '0'.

Fixes: 11e2ab3f ("ARM: omap3: evm: Enable booting 'fitImage' with DEFAULT_FIT_TI_ARGS")
Signed-off-by: Derald D. Woods <woods.technical@gmail.com>