arm: am57xx: Add vendor partition to Android GPT table for eMMC

Add vendor partition to Android GPT table for eMMC.

A Vendor image contains SoC-specific code and configuration.

Prior to Android 8.0, the vendor partition was optional ;
files belonging to these images were placed in boot.img or system.img
with symlinks (such as /vendor >/system/vendor ) when absent.

Android 8.0 makes the vendor partition mandatory

The goal is to modularize Android partitions with standard interface between
the Android Platform (on system.img ) and vendor-provided code(on vendor.img).

This standard interface enables the Android Platform to be updated
without affecting the SoC partitions. This makes it possible to upgrade a
device system.img from Android 8.0 to Android P while other images (such as
vendor.img) remain at Android 8.0. This modularity enables timely
Android platform upgrades (such as monthly security updates )
without requiring SoC/ODM partners to update SoC- and device-specific code.

Signed-off-by: Praneeth Bajjuri <praneeth@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>