drivers: sdhc: add support of Renesas MMC driver

Add basic functionality of Renesas SD/MMC driver. It can be used
for both gen3 and gen4 R-car boards, but tested only with H3ULCB,
Salvator XS M3 and Spider boards. This driver working with SDHC
subsystem.

The driver supports regularal reading/writing throught SD/MMC
controller buffer, DMA mode w/o interrupts and timing tuning.

Add gpio5 and sd0 nodes to h3ulcb and salvator xs which are needed
for working with SD cards. The GPIO node is needed for switching
voltage on SD card through gpio regulator driver.

Notes:
    * the driver doesn't support SPI mode;
    * SCC tuning and DMA mode based on IRQs are enabled by default;
    * an address of a data buffer has to be aligned to 128 bytes if it
      is not, driver will use non-DMA mode automatically;
    * Renesas MMC DMAC doesn't support 64-bit DMA addresses, so for
      case when we have 64-bit xref data address we use non-DMA mode;
    * SD/MMC controller supports block size between 512 and 1 with
      a lot of restrictions, more details you can find in code;
    * support of HS400 mode isn't implemented inside driver.

Signed-off-by: Mykola Kvach <mykola_kvach@epam.com>

dts/bindings/mmc/renesas,rcar-emmc.yaml

@@ -0,0 +1,63 @@
+description: Renesas R-Car eMMC
+
+compatible: "renesas,rcar-mmc"
+
+include: [sdhc.yaml, mmc.yaml, pinctrl-device.yaml, reset-device.yaml]
+
+properties:
+  clocks:
+    required: true
+
+  reg:
+    required: true
+
+  pinctrl-0:
+    required: true
+
+  pinctrl-names:
+    required: true
+
+  max-bus-freq:
+    required: true
+
+  non-removable:
+    type: boolean
+    description: |
+      Non-removable slots (like eMMC), which are assumed to always be present,
+      will affect the `sdhc_card_present` call. This call will always return
+      true if this property exists for the node.
+
+  mmc-sdr104-support:
+    type: boolean
+
+  cd-gpios:
+    type: phandle-array
+    description: Card Detect pin
+
+  pwr-gpios:
+    type: phandle-array
+    description: Power pin
+
+  vmmc-supply:
+    type: phandle
+    description: |
+      Supply for the card power
+
+  vqmmc-supply:
+    type: phandle
+    description: |
+      Supply for the bus IO line power, such as a level shifter.
+      If the level shifter is controlled by a GPIO line, this shall
+      be modeled as a "regulator-fixed" with a GPIO line for
+      switching the level shifter on/off.
+
+  bus-width:
+    type: int
+    default: 1
+    description: |
+        Bus width for SDMMC access, defaults to the minimum necessary
+        number of bus lines
+    enum:
+      - 1
+      - 4
+      - 8