OvmfPkg/OvmfPkgX64: Expose DEBUG_TO_MEM as a build option OvmfPkgX64.dsc has several build options, but some are missing from the top definition list. This makes it difficult for users to identify all available configuration flags. Add DEBUG_TO_MEM to the [Defines] section with a default value of FALSE to improve visibility. This change has no functional impact. Signed-off-by: Richard Lyu <richard.lyu@suse.com>