Add guards around code that is specific to dynamically-loaded groups
Add guards around code that is specific to dynamically-loaded groups

For some curves (semi-coincidentally, short Weierstrass curves), the
ECP module calculates some group parameters dynamically. Build the
code to calculate the parameters only if a relevant curve is enabled.
This fixes an unused function warning when building with only
Montgomery curves.

Signed-off-by: Gilles Peskine <f829db02715a0ea34b7c8e25097dae9e3517e831@arm.com>

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