dev: Fix std::min type mismatch in reg_bank.hh

[BobbyRBruce]

#386 included two cases in "src/dev/reg_bank.hh" where std:: min was used to compare a an integer of type size_t and another of type Addr. This causes an error on my Apple Silicon Mac as the comparison between an "unsigned long" and an "unsigned long long" is not permitted. To fix this issue this patch changes reg_size from size_t to Addr, as well as it the types of the values it was derived from and the variable used to hold the return from the std::min calls. While not completely correct typing from a labelling perspective (reg_bytes is not an address), functions in "src/dev/reg_bank.hh" already abuse Addr in this way frequently (for example, bytes in the write function).

[BobbyRBruce]

For the curious, it seems like The C++ stdlib provided by MaxOSX.sdk enforces demands equal type/bitwidth for the integers passed to std:min:

In file included from build/ALL/python/_m5/param_IdeDisk.cc:17:
In file included from src/dev/storage/ide_disk.hh:52:
In file included from src/dev/storage/ide_ctrl.hh:40:
src/dev/reg_bank.hh:984:36: error: no matching function for call to 'min'
          const size_t reg_bytes = std::min(reg_size, bytes - done);
                                   ^~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__algorithm/min.h:40:1: note: candidate template ignored: deduced conflicting types for parameter '_Tp' ('size_t' (aka 'unsigned long') vs. 'Addr' (aka 'unsigned long long'))
min(const _Tp& __a, const _Tp& __b)

I'm surprised it doesn't upcast in these cases.

[powerjg]

I don't like to use Addr this way, but given the rest of the code does use Addr as a size, I think this is fine.