ARM: dts: keystone: update for supporting K2L/K2E EVMs

This patch add compatibility strings for k2hk, k2l and k2e EVMs

Cc: Olof Johansson <olof@lixom.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>