package/ti-cgt-pru: specify need for 32-bit host libraries

package/ti-cgt-pru: specify need for 32-bit host libraries

Fixes:
http://autobuild.buildroot.net/results/787/7875507cc1009c9a495695f9d9ecb974530a3f72

The downloaded source for the ti-cgt-pru package is an installer that
requires 32-bit host libraries for extraction. Specify this dependency
in the package configuration [1].

[1] http://lists.busybox.net/pipermail/buildroot/2020-January/271416.html

Signed-off-by: Ash Charles <ashcharles@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>