Removed hack that did the R_SHIFT of unsigned numbers, no longer need

Removed hack that did the R_SHIFT of unsigned numbers, no longer need
to do this as I have changed to using PDTI's as the bases for the vm
system layout.

Eliminate constants SYSPDROFF and SYSPDREND, now use NKPTE to control the size
of the kernel virtual space.

Eliminate constant PDRPDROFF, now use PDTDTPI to control location of PTD,
PTDmap and PTDpde

Eliminate constant APDRPDROFF, now use APTDPTDI to control location of APTD,
APTDmap and APTDpde.

Still need to fix Sysmap location (it is still a constant).

.globl statements are now consistent with respect to <comma><space>, the
<space> being removed from all .globl statements.

Document the fillkpt macro as to what registers control what.

Fix some comments that went past column 80, and clean/line some others up.

Remove constand for _Crtat, now use KERNBASE+constant, this still needs work.

Replace constants for offsets of sigcode parameters with symbolic names
from assym.s

Mark the sigreturn() call with XXX since we use the hardcoded constant
for the system call number, this is bogus and should be a #define or
something some place!

The kernel before and after this change was verified with cmp, not one
byte changed.  These are all cosmetic clean up changes that makes the
code more correct and easier to move the kernels virtual address space
and size.