Adds to footprint.sh MBEDTLS_NO_PLATFORM_ENTROPY
Adds to footprint.sh MBEDTLS_NO_PLATFORM_ENTROPY

For baremetal builds MBEDTLS_NO_PLATFORM_ENTROPY must now be set to avoid the
build failing.

Fixes #449.

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