ASoC: rt5651: Remove is_sys_clk_from_pll()

is_sys_clk_from_pll() is used as a snd_soc_dapm_route.connected callback,
checking RT5651_GBL_CLK to determine if the sys-clk is PLL1 and thus the
PWR_PLL bit in reg PWR_ANLG2 must be set.

RT5651_GBL_CLK is changed by rt5651_set_dai_sysclk(), which gets called by
the pre_pmu / post_pmd functions of the "Platform Clock" dapm-supply.

This creates an ordering issue, during a dapm transition first all
connected() callbacks are called to build a list of supplies to enable
and then the complete list is walked to enable the supplies. Since the
connected() check happens before enabling any supplies,
is_sys_clk_from_pll() ends up deciding if the PWR_PLL bit should be set
based on the state the "Platform Clock" supply had *before* the transition.
This sometimes results in PWR_PLL being off, even though *after* the
transition PLL1 is configured as sys-clk.

This commit removes is_sys_clk_from_pll() instead simply setting / clearing
PWR_PLL in rt5651_set_dai_sysclk() based on the selected sys-clk, which
fixes this and as a bonus results in a nice cleanup.

Tested-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mark Brown <broonie@kernel.org>