Add RTC feature for Micro8088

[spark2k06]

• Detect and use RTC (DS12885/7) for Micro8088

[skiselev]

Thank you for your code contribution!
I've added RTC auto-detect functionality in bd82671
using parts of your code. I haven't tested it just yet.

I would like to share some feedback considering the 8088 BIOS development, and the reason I couldn't merge your commit directly:

• The BIOS supports multiple 80x86/80x88 configurations. And therefore it should be highly configurable at the build time. For example, do not assume that everyone is going to have an RTC or need RTC functionality. Use ifdef/endif around the optional code.
• The machines' configurations are defined in config.inc. When adding an optional feature, it can be enabled from that file. Depending on circumstances a new machine configuration can be created, or a define can be added to an existing machine configuration.
• The setloc macros are there for the compatibility reason: Some software (especially BIOS extensions) call BIOS entry points directly, without using interrupt instructions. Do not modify setlocs. If the modified code does not fit, it should be moved elsewhere, e.g. to the beginning of the BIOS code. All setlocs are limited to the last 8 KiB of the address space.

[spark2k06]

I agree on all your annotations. I have added a new pull request taking advantage of the configuration of config.inc to facilitate the user to change CMOS_CONTROL_B_CONFIG in the RTC. Among other things, you may want to use the DSE:

#5