refactor(measured boot): remove weak definition of plat_get_measured_boot_data()
refactor(measured boot): remove weak definition of plat_get_measured_boot_data()

Weak definitions are confusing and should be avoided if possible.
Thus, turn plat_get_measured_boot_data() into a strong definition that
platforms must provide (if they need measured boot).

We could have moved the old weak implementation under plat/common as a
sane, default implementation that platforms may pull in if it suits
them. However, this implementation right now simply measures BL2,
which is not enough to get a complete measured boot flow, so this
patch just removes it.

This change only affects the Arm FVP platform, as no other upstream
platform implements measured boot at the moment.

Change-Id: If8680a39ae0ef1044ee981315439d5e0c8461229
Signed-off-by: Sandrine Bailleux <4b69fcfca8da45b0c11ecda5434c5da526575d9d@arm.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware