Platform/ARM/JunoPkg: Switch to MdeModulePkg/Universal/Metronome driver

The MetronomeDxe driver uses the PCD PcdMetronomeTickPeriod to calculate
how many ticks to wait in MicroSecondDelay. Given that the timer clock
on Juno runs at 50 MHz, it ticks every 20 ns; therefore, a setting of
1000 is wrong: for example it causes a call to gBS->Stall (1) to take
10 us.

The driver in MdeModulePkg/Universal/Metronome assumes the clock ticks
at least every 100 ns, which is the minimum allowed by the Metronome
protocol. Since that's the case on Juno, switch from
EmbeddedPkg/MetronomeDxe to MdeModulePkg/Universal/Metronome.

Signed-off-by: Rebecca Cran <rebecca@quicinc.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>