Rename --arm-gcc-prefix to --arm-none-eabi-gcc-prefix
Rename --arm-gcc-prefix to --arm-none-eabi-gcc-prefix

This is supposed to be for GCC (or a compiler with a compatible
command line interface) targeting arm-none-eabi, so name it
accordingly.

Signed-off-by: Gilles Peskine <f805f64266d288fc5467baa7be6cd0ff366f477b@arm.com>

ARMmbed/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls