armsr: rename from armvirt

armsr: rename from armvirt

Now that the armvirt target supports real hardware, not just
VMs, thanks to the addition of EFI, rename it to something
more appropriate.

'armsr' (Arm SystemReady) was chosen after the name of
the Arm standards program.

The 32 and 64 bit targets have also been renamed
armv7 and armv8 respectively, to allow future profiles
where required (such as armv9).

See https://developer.arm.com/documentation/102858/0100/Introduction
for more information.

Signed-off-by: Mathew McBride <matt@traverse.com.au>