Making top-level parameters localparams

### Description

Many of the top-level parameters are derived from HJSON definitions but could be unintentionally overridden.
We proposed that we should local parameters whenever possible, i.e., for parameters like SRAM size that should not be overridable.
This would make the top hjson essentially the single source of truth for these parameters.
However, some parameters should remain top-level parameters (e.g., external signal widths, FPGA-specific values, etc).

To do this, we must first review all parameters and determine their appropriate exposure level.

(Note: This is coming from the Multi-Top WG discussion on July 1st)