Check snprintf() return value for errors.

Make microblaze_cpu_get_desc() directly return snprintf() error code if
ret < 0. Otherwise, if the return value is greater than or equal to size,
the resulting string is truncated, so return -ENOSPC.

Fixes: 816226d27e ("cpu: add CPU driver for microblaze")
Signed-off-by: Ovidiu Panait <ovpanait@gmail.com>
Link: https://lore.kernel.org/r/20220829170205.1274484-2-ovpanait@gmail.com
Signed-off-by: Michal Simek <michal.simek@amd.com>

Add a basic CPU driver that retrieves information about the microblaze CPU
core. cpu_ops handlers are implemented so that the "cpu" command can work
properly:

U-Boot-mONStR> cpu list
  0: cpu@0      MicroBlaze @ 50MHz, Rev: 11.0, FPGA family: zynq7000
U-Boot-mONStR> cpu detail
  0: cpu@0      MicroBlaze @ 50MHz, Rev: 11.0, FPGA family: zynq7000
        ID = 0, freq = 50 MHz: L1 cache, MMU

Note: cpu_ver_lookup[] and family_string_lookup[] arrays were imported from
linux.

Signed-off-by: Ovidiu Panait <ovpanait@gmail.com>
Link: https://lore.kernel.org/r/20220531181435.3473549-14-ovpanait@gmail.com
Signed-off-by: Michal Simek <michal.simek@amd.com>