Use a switch instead of an array. The array was very hollow for some enum
types such as mbedtls_ssl_protocol_version (which formerly used small
values, but switched to using the protocol encoding as enum values in Mbed
TLS 3.2.0). Optimizing compilers know how to compile a switch into a lookup
table when the range warrants it.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
