Can I use keil 5.11a for stm32 with my own drivers? or I have to use keil software packs for stm32?
what about startup assembly file and other cortex m related file?
You are in serious trouble!
Drivers for embedded processors normally don't have any unifying API to translate them into some generic "PC-class" devices. Any extra glue adds extra code size and adds extra delays - and also requires the specific strengths of a specific chip to be ignored to have it emulate basic functionality.
With older generation embedded processors, people often didn't even try to write any drivers - they wrote the driver code inlined in their application code just to cut some instruction cycles here and there.