clk: davinci: pll-dm355: drop pll2_sysclk2

This removes pll2_sysclk2 from the TI DM355 clock driver. This SoC
doesn't have such a clock. Also, SYSCLK_ALWAYS_ENABLED is transferred
to pll2_sysclk1 since it drives the DDR and doesn't have another
mechanism to keep it on.

Reported-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: David Lechner <david@lechnology.com>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20180525181150.17873-2-david@lechnology.com