OvmfPkg/PlatformDebugLibIoPort: list "DebugLibDetect.h" in the INF files

Among other things, "DebugLibDetect.h" declares the
PlatformDebugLibIoPortFound() function. The function is called from
"DebugLib.c", which is included in both library instances. The function is
defined separately per library instance, in "DebugLibDetectRom.c" and
"DebugLibDetect.c", respectively.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Suggested-by: Michael Kinney <michael.d.kinney@intel.com>
Ref: http://mid.mail-archive.com/E92EE9817A31E24EB0585FDF735412F56327F7D3@ORSMSX113.amr.corp.intel.com
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>