docs(morello): update the boot sequence according to the TBBR boot flow

The boot sequence mentioned in the documentation referred to an older
boot flow. This patch updates the boot sequence to the TBBR boot flow
that is currently being followed.

Signed-off-by: Deepthi Peter <deepthi.peter@arm.com>
Change-Id: I183458cea6d43dcf8acba2e0422920ab5541fdfc
1 file changed