Added LGT MCU cpu duty support.

[rgwan]

No description provided.

[AndreiCherniaev]

Dear @rgwan can you sync your code with last version of v-usb?

[starkjohann]

Since Andrei asked to merge with the latest version: The merge should be simple, but I don't want to add a second assembler implementation for each clock speed. I would prefer a minimal conditional change with macros. The main difference seems to be that push, pop, ld and jumps take one cycle instead of two. We could add a macro lgt_delay which defines to no delay on AVR and a single NOP on LGT. That way the code could be shared and we would not need to update two files when something changes.