Implement half of bootup_misc_mmio()

Implement a few TODOs with CAR driver.

Rewrite the memory map-related code... ...

...other style fixes, etc.

fuse: simplify checks in fuse_get_reserved_odm and fuse_get_spare_bit (#54) ...

A separate variable isn't particularly necessary here, and given that the type
is unsigned, we only need to test the upper bound.

This also resolves two -Wtype-limits warnings

Move source files to src/, add Makefile, fix all build and linkage errors, etc.