pps-tools: new package

Added pps-tools package to add support to the ntpd for a
pps source (requires timepps.h from pps-tools as part of ntpd
build).

[Thomas:
  - Use $(TARGET_MAKE_ENV) at install time.
  - Alphabetic ordering in package/Config.in, noticed by Jerzy
    Grzegorek.]

Signed-off-by: Bryan Brinsko <bryan.brinsko@rockwellcollins.com>
Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>