RSE: RD-V3: rename 'RD-Fremont' plat to 'RD-V3'

Change all occurances of RD-Fremont to RD-V3 to align with the official
platform name.

Signed-off-by: Arnold Gabriel Benedict <arnoldgabriel.benedict@arm.com>
Change-Id: I8581cfcb2bc2def279e002888b8a951b3e7935e7