arm: dra76: fastboot: extend cpu type for getvar command

'commit fa24eca1 ("omap: Add routine for setting fastboot variables")'
adds initial support and usage of "fastboot getvar" command
for DRA75x and DRA72x devices.

and
'commit 0f9e6aee ("arm: dra76: Add support for ES1.0 detection")'
adds initial dra76 device definition

This patch is to extend usage of "fastboot getvar" for DRA76 device.

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