Convert CONFIG_ARMV8_SWITCH_TO_EL1 to Kconfig

This converts the following to Kconfig:
   CONFIG_ARMV8_SWITCH_TO_EL1

Cc: Alex Nemirovsky <alex.nemirovsky@cortina-access.com>
Cc: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tien Fong Chee <tien.fong.chee@intel.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Michal Simek <michal.simek@xilinx.com>