mt76: mt7915: add more MIB registers

Add register definitions and read & accumulate them in
the mib polling logic.  Note that some registers should not
be read since firmware is already reading them.  If driver
reads those, they will be cleared-on-read, and so the firmware
stats will be incorrect.

For these 'do-not-read' stats, add them to the registers definition
so that other developers can be aware of these constraints, but do
not actually read them in the driver.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>