board: samsung: fix menu entries for a{3,7}y17lte

a7y17lte is called SM-A720F, and a3y17lte SM-A320F.  a3y17lte also
should select PINCTRL_EXYNOS78x0, not the (non-existent)
PINCTRL_EXYNOS7880, and it has an Exynos 7870 SoC and not 7880.

Fixes: 3e2095e9 ("board: samsung: add support for Galaxy A series
of 2017 (a5y17lte)")
Signed-off-by: Henrik Grimler <henrik@grimler.se>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>