clk: at91: utmi: add timeout for utmi lock

clk: at91: utmi: add timeout for utmi lock

In case the slow clock is not properly configured, the UTMI clock
cannot lock the PLL, because UPLLCOUNT will "wait X slow clock cycles".
In this case U-boot will loop indefinitely.
Added a timeout in this case, to start U-boot even if UTMI clock is
not enabled, so the user can use different media if needed, or investigate.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>