arm64: dts: meson: add rtc aliases to meson-khadas-vim3.dtsi

Tweak the node name to make it aliasable, then add aliases for the
on-board RTC chip and meson-vrtc timer so they probe as rtc0 and
rtc1 respectively.

before:

VIM3:~ # dmesg | grep rtc
[    3.622530] meson-vrtc ff8000a8.rtc: registered as rtc0
[    3.622574] meson-vrtc ff8000a8.rtc: setting system clock to 1970-01-01T00:00:03 UTC (3)
[    3.646936] rtc-hym8563 0-0051: no valid clock/calendar values available
[    3.647125] rtc-hym8563 0-0051: registered as rtc1
[    3.852382] rtc-hym8563 0-0051: no valid clock/calendar values available

after:

VIM3:~ # dmesg | grep rtc
[    3.583735] meson-vrtc ff8000a8.rtc: registered as rtc1
[    3.633888] rtc-hym8563 0-0051: no valid clock/calendar values available
[    3.634120] rtc-hym8563 0-0051: registered as rtc0
[    3.635250] rtc-hym8563 0-0051: no valid clock/calendar values available
[    3.635267] rtc-hym8563 0-0051: hctosys: unable to read the hardware clock
[    3.852632] rtc-hym8563 0-0051: no valid clock/calendar values available

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20201124145338.17137-1-christianshewitt@gmail.com