arm64: dts: meson: a1: add eMMC controller and its pins

arm64: dts: meson: a1: add eMMC controller and its pins

The definition is inspired by a similar one for AXG SoC family.
'sdio_pins' and 'sdio_clk_gate_pins' pinctrls are supposed to be used as
"default" and "clk-gate" in board-specific device trees.

During initialization 'meson-gx' driver sets clock to safe low-frequency
value (400kHz). However, both source clocks ("clkin0" and "clkin1") are
high-frequency by default, and using of eMMC's internal divider is not
enough to achieve so low values. To provide low-frequency source,
reparent "sd_emmc_sel2" clock using 'assigned-clocks' property.

Signed-off-by: Jan Dakinevich <yvdakinevich@sberdevices.ru>
Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20230823213630.12936-11-ddrokosov@sberdevices.ru
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>