uvm_reg_map::get_size doesn't remove unmappd reg/mem

[GuangMing34]

uvm_reg_map::get_size still includes unmapped mem/register since it doesn't check the unmapped flag.

https://github.com/accellera-official/uvm-core/blob/main/src/reg/uvm_reg_map.svh#L1289

[mstrickland-mrvl]

We will ask the IEEE WG to decide whether it should be the case that unmapped is excluded

[GuangMing34]

If I want to calculate the mapped size of a reg_block, are there any suggested methods to do it?