kernel: Enhance naming of memory pool configuration options

Replaces confusing (and excessively long) configuration option
names with more intuitive names. Also enhances the description
of each option to clarify its use.

Change-Id: If4d4541407627482b1e90302cfc9df3bc8130d44
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>