build-*: update ARM-TF variables to TF-A in scripts and config files

Update all variable references of Arm Trusted Firmware to Trusted
Firmware-A (TF-A). This is for consistency with and disambiguation from
Trusted Firmware-M (TF-M) [1].

[1]: https://github.com/ARM-software/arm-trusted-firmware/commit/4def07d5352893a33af18b04795f875fabff14de



Signed-off-by: Tony Nadackal <tony.nadackal@arm.com>
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I8de6f7212c1e5bc701bf4ad311c0b6695e66f91f