[TESTS] Rename basic test to basic firmware

Our basic test for arm32 guest is more than just a test code. It is more
of a firmware/bootloader for various arm32 guest hence, with this patch
we start referring basic test as basic firmware.

The changes done by this patch are as follows:
1. Rename "basic test" to "basic firmware" everywhere
2. Rename arm_test.bin to firmware.bin everywhere
3. Rename arm_test.elf to firmware.elf everywhere
4. Rename prompt from "arm-test#" to "basic#"

Signed-off-by: Anup Patel <anup@brainfault.org>