C-CMIS PM API and memory map support

[nkanchi-nexthop]

Description

Adds C-CMIS Page 3Ah support and completes the missing Page 35h fields following C-CMIS 1.4. Adds the corresponding register field constants to fields/consts.py, a new page3a.py memory map page, and wires it into the page registry.

Motivation and Context

• The memory map was missing several coherent PM registers defined in C-CMIS 1.4 (page 35h bytes 212-241), so these newer optical PMs for coherent modules could not be read.
• The memory map was missing page 3Ah entirely, so hosts couldn't read host-side FEC/frame performance counters

How Has This Been Tested?

• Ran tests/sonic_xcvr/test_ccmis.py and passed for page35.py and the new page3a.py. Verified each new register's byte offset, size, signedness, and scale factor against the corresponding tables (Table 15, Table 18) in C-CMIS 1.4.
• Verified on a DUT with changes from following PRS: C-CMIS PM memory maps, C-CMIS API, C-CMIS PM STATE_DB, C-CMIS PM CLI.

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