Fix qpu decorator not to override the original function name and doc

[Terminus-IMRC]

Without functools.wraps, the name and the doc of a function to be decorated will be lost. This PR fixes that.

Example code:

#!/usr/bin/env python3

from videocore.assembler import qpu

@qpu
def qpu_code(asm):
    nop()
    exit(interrupt = True)

print(qpu_code.__name__)

Before the change in this PR, the code prints decorated, which is the name of the decorator. After the change, the output will be qpu_code, which is desired.

[nineties]

Thanks!

[Terminus-IMRC]

Thanks for merging!