New interface overlays

src/en/overlay/iface-dpi.md

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+<!--
+---
+class: interface
+type: pinout
+name: DPI
+description: Raspberry Pi DPI pins
+pincount: 22
+pin:
+  '0':
+    name: CLK
+  '1':
+    name: DEN
+  '2':
+    name: V-SYNC
+  '3':
+    name: H-SYNC
+  '4':
+    name: Blue 2
+  '5':
+    name: Blue 3
+  '6':
+    name: Blue 4
+  '7':
+    name: Blue 5
+  '8':
+    name: Blue 6
+  '9':
+    name: Blue 7
+  '10':
+    name: Green 2
+  '11':
+    name: Green 3
+  '12':
+    name: Green 4
+  '13':
+    name: Green 5
+  '14':
+    name: Green 6
+  '15':
+    name: Green 7
+  '16':
+    name: Red 2
+  '17':
+    name: Red 3
+  '18':
+    name: Red 4
+  '19':
+    name: Red 5
+  '20':
+    name: Red 6
+  '21':
+    name: Red 7
+-->
+#DPI - Display Parallel Interface
+
+###DPI (Display Parallel Interface) is a 24-bit parallel interface with 28 clock and synchronisation signals. The Pi uses a cut-down, 6-bit, 22 pin version omitting the least significant R, G and B colour bits.
+
+DPI, combined with a simple adaptor consisting of 20 resistors, allows you to add a VGA connector to the Pi which supports resolutions from 640 x 480 up to 1920 x 1024 at 60fps and 6bits per channel.

src/en/overlay/iface-pcm.md

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+<!--
+---
+class: interface
+type: pinout
+name: PCM
+description: Raspberry Pi PCM pins
+pincount: 4
+pin:
+  '18':
+    name: CLK
+  '19':
+    name: FS
+  '20':
+    name: DIN
+  '21':
+    name: DOUT
+-->
+#PCM - Pulse-code Modulation
+
+###PCM (Pulse-code Modulation) is a digital representation of sampled analog. On the Raspberry Pi it's a form of digital audio output which can be understood by a DAC for high quality sound.

src/en/overlay/iface-sd.md

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+<!--
+---
+class: interface
+type: pinout
+name: SD
+description: Raspberry Pi SD0/SD1 pins
+pincount: 4
+pin:
+  '22':
+    name: CLK
+  '23':
+    name: CMD
+  '24':
+    name: DAT0
+  '25':
+    name: DAT1
+  '26':
+    name: DAT2
+  '27':
+    name: DAT3
+-->
+#SD - SD Card Interface
+
+###SD is the SD host/eMMC interface on the Raspberry Pi. SD host signals are normally used for the microSD slot.
+
+These pins are "SD host" on Alt0 and "eMMC" on Alt3.