OvmfPkg: AcpiPlatformDxe: extract common entry point

OvmfPkg: AcpiPlatformDxe: extract common entry point

Currently the entry point functions of both driver builds
(AcpiPlatformDxe.inf and QemuFwCfgAcpiPlatformDxe.inf) directly contain
the logic that is different between the two builds.

Because we're going to restructure the entry point logic soon, we'd have
to duplicate the same new code between both entry point functions.

Push down the logic in which they differ to a new function:
- InstallAcpiTables() [AcpiPlatform.c]
- InstallAcpiTables() [QemuFwCfgAcpiPlatform.c]

and extract a common entry point function:
- AcpiPlatformEntryPoint() [EntryPoint.c]

which we can soon modify without code duplication.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16885 6f19259b-4bc3-4df7-8a09-765794883524