sysutils/powerdxx: Update to 0.2.5

• Update to 0.2.5, fixes bug in 12-CURRENT [1]
• Update pkg-plist
• Update LICENSE (BSD2CLAUSE -> ISCL)

[1] https://github.com/lonkamikaze/powerdxx/releases/tag/0.2.5

Reviewed by: mat, koobs
Approved by: koobs (mentor)
Differential Revision: https://reviews.freebsd.org/D8698