This patch removes the FIRST_RESET_HANDLER_CALL build flag and its
use in ARM development platforms. If a different reset handling
behavior is required between the first and subsequent invocations
of the reset handling code, this should be detected at runtime.

On Juno, the platform reset handler is now always compiled in.
This means it is now executed twice on the cold boot path, first in
BL1 then in BL3-1, and it has the same behavior in both cases. It is
also executed twice on the warm boot path, first in BL1 then in the
PSCI entrypoint code.

Also update the documentation to reflect this change.

NOTE: THIS PATCH MAY FORCE PLATFORM PORTS THAT USE THE
FIRST_RESET_HANDLER_CALL BUILD OPTION TO FIX THEIR RESET HANDLER.

Change-Id: Ie5c17dbbd0932f5fa3b446efc6e590798a5beae2