Overestimate binary size for microTVM compiled binaries. (#5590)

Overestimate binary size for microTVM compiled binaries. (#5590)

* Overestimate binary size for microTVM compiled binaries.

 * Currently uTVM binary section sizes are computed by summing the
   sizes of all symbols in the section.
 * This method produces errors because it presumes the linker works in
   a particular way, rather than analyzing the linked output.
 * As we intend to move away from linking inside TVM (RFC
   forthcoming), just using this stopgap to make forward progress
   until then.

* address weberlo comments

* fix regression (use 64 bit word size)