arm: dra7xx: Define Android partition table

"fastboot oem format" command reuses "gpt write" command, which in turn
requires correct partitions defined in $partitions variable. This patch
adds such definition of Android partitions for DRA7XX EVM board.

By default $partitions variable contains Linux partition table. In order
to prepare Android environment one can run next commands from U-Boot
shell:

    => env set partitions $partitions_android
    => env save

After those operations one can go to fastboot mode and perform
"fastboot oem format" to create Android partition table.

While at it, enable CONFIG_RANDOM_UUID to spare user from providing
UUIDs for each partition manually.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>