sh/cb2replay: Use a shell variable to denote hex characters

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
util/cb2replay: Convert delay loops to single delay function

Successive reads from port 0x3f54 indicate a delay loop. This seems
to correspond to a 50MHz timer. Convert this access pattern to a
radeon_delay() function.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
util/cb2replay: Group timer control writes in radeon_delay()

Delay loops always start with a write access to what appears to be
the timer control register. Group that access in radeon_delay().

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>