Clean up some bsd.crunchgen.mk issues.

• Remove handling of 'make -P' since that is for fmake only.
• Add '+' where appropriate for sub-make calls.
• Pass MK_TESTS=no to all of the sub-makes to prevent recursing into test directories for targets such as 'obj', 'clean', 'depend', etc.

Sponsored by: EMC / Isilon Storage Division