Correct port files used for FreeRTOS

Note that cortex-m52 will use the same path as cortex-m55 as there are
no separate port files for cortex-m52.

Add required configENABLE_MVE option to the default config.

Signed-off-by: Jonny Svärd <jonny.svaerd@arm.com>
Change-Id: I7827bdabcb7250f8838c150ba3094cfd86d9b14a