sing 'sleep', the implementation was a delay.
   I've marked some places with XXX where we should probably be using
   msleep instead.  They need to be audited to be sure we can sleep in
   that context.
 - Replace DvcDelayMicroSecond with udelay.
 - Replace DvcDelayNanoSecond with udelay too.
   All callers were multiples of 1000.
 - Remove DvcEnterCritical and DvcLeaveCritical.
   These functions are no-ops, and as the comments said, the spinlock
   protects the critical sections.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
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