flow3r_bsp: new captouch driver

This reimplements components/captouch into a separate BSP-based captouch
driver.

New features:

 1. Interrupt-driven, which seems to improve performance.
 2. Has ability to run multiple sequences one after another on the
    AD7147. This is needed to support 13 channels on the bottom captouch
    controller. However, this seems to be currently broken (see BUG).