Hello,
Actually, the driver source is on the SDK, for example in SDK 2.14 is under:
SDK_2_14_0_MCIMX93-EVK/middleware/ethos-u-core-software/core_driver/src/ethosu_driver.c
and
SDK_2_14_0_MCIMX93-EVK/middleware/ethos-u-core-software/core_driver/include/ethosu_driver.h
Best regards,
Salas.