config: rename RD-Fremont to RD-V3

Neoverse Reference Design platform RD-Fremont has been renamed to RD-V3
and all corresponding references have been changed.

Signed-off-by: Jaylyn Ren <Jaylyn.Ren2@arm.com>
Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
Change-Id: I2778c7cff51a15a41f75bf510839874a47a818a8