ARM: ep93xx: ts72xx: cosmetic: Add some description to ts72xx code

This patch extends readability of ts72xx.c code.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>