OvmfPkg: disable deprecated interfaces

OvmfPkg: disable deprecated interfaces

At this point no code in OvmfPkg (and apparently no code outside of
OvmfPkg that OVMF depends on) uses the deprecated APIs, so we can disable
them in the platform DSC files:

BaseLib:
- StrCpy
- StrnCpy
- StrCat
- StrnCat
- UnicodeStrToAsciiStr
- AsciiStrCpy
- AsciiStrnCpy
- AsciiStrCat
- AsciiStrnCat
- AsciiStrToUnicodeStr

PcdLib:
- PcdSet8
- PcdSet16
- PcdSet32
- PcdSet64
- PcdSetPtr
- PcdSetBool
- PcdSetEx8
- PcdSetEx16
- PcdSetEx32
- PcdSetEx64
- PcdSetExPtr
- PcdSetExBool

UefiLib:
- GetVariable
- GetEfiGlobalVariable

Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>