microblaze: Convert axi timer to DM driver

Move axi timer driver from Microblaze to generic location.
Origin implementation was irq based with counting down timer.

CONFIG_TIMER drivers are designed differently that timer is free running up
timer with automatic reload without any interrupt.
Information about clock rates are find out in timer_pre_probe() that's why
there is no need to get any additional information from DT in the driver
itself (only register offset).

Signed-off-by: Michal Simek <michal.simek@amd.com>
Tested-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Link: https://lore.kernel.org/r/6c12fc86bbc1f17d05c25018862e7b7b03346b36.1654684731.git.michal.simek@amd.com