tg3: Override clock, link aware and link idle mode during NVRAM dump

When cable is not present the clock speed of some of the devices is
reduced based upon power saving mode setting in NVRAM. Due to this
NVRAM reads take long time to complete as a result CPU soft lockup
message is seen. Fix is to override clock, disable link aware and link
idle modes before NVRAM reads and restore them back after the reads
are complete. During this period also check if the thread needs to be
rescheduled and if there are any signals to handle.

Also decrease the NVRAM command execution timeout value to 1ms.

Signed-off-by: Prashant Sreedharan <prashant@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>