This patch extends the protection domain framework with a third plugin
that is a hybrid of the previous two. The hardware task switching
mechanism has a strictly-defined format for TSS data structures that
causes more space to be consumed than would otherwise be required.
This patch defines a smaller data structure that is allocated for each
protection domain, only requiring 32 bytes instead of 128 bytes. It
uses the same multi-segment memory layout as the TSS-based plugin and
leaves paging disabled. However, it uses a similar mechanism as the
paging plugin to perform system call dispatches and returns.
For additional information, please refer to cpu/x86/mm/README.md.
