ArmVirtPkg: Use SerialDxe in MdeModulePkg instead of EmbeddedPkg

ArmVirtPkg: Use SerialDxe in MdeModulePkg instead of EmbeddedPkg

Beyond just changing the directly related lines in the FDF and DSC files,
we have to adapt the EarlyFdtPL011SerialPortLib and FdtPL011SerialPortLib
instances as well, in the same patch. This is because the EmbeddedPkg
driver expects the SerialPortSetAttributes(),
SerialPortSetControl() and SerialPortGetControl() functions from
SerialPortExtLib, while the MdeModulePkg driver expects them from
SerialPortLib itself.

We cannot implement these functions in ArmVirtPkg's SerialPortLib
instances *before* flipping the driver, because it would cause double
function definitions in the EmbeddedPkg driver. We also can't implement
the functions *after* flipping the driver, because it would cause
unresolved function references in the MdeModulePkg driver. Therefore
we have to implement the functions simultaneously with the driver
replacement.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18973 6f19259b-4bc3-4df7-8a09-765794883524