[u-blox][r510] fixes EHS timing when modem locks up while in Power Saving mode

[technobly]

Problem

• u-blox R510 modems have a reduced clock timing when in Power Saving mode, and if they should lock-up in that mode and require recovery intervention with the Emergency Hardware Shutdown (EHS) procedure, the standard documented timing will not recover them. Instead, timings given by u-blox for a 1/4 clock rate shall be used.

Solution

• Reduce the number of reset attempts from 10 to 3 before attempting EHS to help speed up recovery.
• Toggle between standard and extended EHS timing when attempting EHS.

Steps to Test

• Tested on a device that was in this state and it recovered.