Add AUTO_HUGEPAGE feature to disable writing to nr_hugepages

[Spudz76]

Sometimes there is need to set/limit hugepages to a smaller amount (up to for example 40 which covers most algos) but do not want the full RandomX allocation (not enough memory, other activities require slack space, only running one of 12 cores anyway so who cares about the speedup for a single-thread calm side mining, etc). But when running as root for MSR access or other reasons the automatic reservation grabs more hugepages.

This adds a compile-time feature to disable writing to nr_hugepages, so that the described use-case works nicely (reserve your own or suffer perhaps intentionally without enough, like older versions). Compile-time was easier to wire and as a power user feature it didn't seem like adding to main config made any sense. It can be converted to an argument/config item later if it appears to be a useful medium-power-user (power-noob?) feature. Also I didn't feel like wiring all that and adding it to docs lol.

Note the default is ON which means be the same as it has been (yes, do autoreserve) and intentionally setting it OFF causes no-writing mode (like old versions).