[MIPS] BCM1250: TRDY timeout tweaks for Broadcom SiByte systems

 It was obesrved that at least one older PCI card predating the
requirement for the TRDY signal to respond within 16 clock ticks actually
does not meet this rule nor even the power-on defaults of the PCI bridges
found in development systems built around the Broadcom SiByte SOCs.  Here
is a patch that bumps up the timeout to the highest finite value supported
by these chips, which is 255 clock ticks.  The bridges affected are the
SiByte SOC itself and the SP1011.
    
 This change does not effectively affect systems only having PCI option
cards installed that meet the TRDY requirement of the current PCI spec.
The rule was introduced with PCI 2.1, so any older card may make the
system affected.  If this is the case, performance of the system will
suffer in return for the card working at all.  If this is a concern, then
the solution is not to use such cards.
    
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

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