clk: mediatek: Mark bus and DRAM related clocks as critical

Currently, DRAM-related clocks are not marked with CLK_IS_CRITICAL
for MT6797. This causes memory corruption when the system is
booted without clk_ignore_unused.
This patch marks MUX ddrphycfg_sel as well as gates infra_dramc_f26m
and infra_dramc_b_f26m as CLK_IS_CRITICAL.

Signed-off-by: Jasper Mattsson <jasu@njomotys.info>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>