mmc: sdhci-iproc: Add brcm, sdhci-iproc compat string in bindings document

Adds brcm,sdhci-iproc compat string to DT bindings document for
the iProc SDHCI driver.

Signed-off-by: Anup Patel <[e-mail]>
Signed-off-by: Scott Branden <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

Documentation/devicetree/bindings/mmc/brcm,sdhci-iproc.txt

···
 - compatible : Should be one of the following
 	       "brcm,bcm2835-sdhci"
 	       "brcm,sdhci-iproc-cygnus"
+	       "brcm,sdhci-iproc"
+
+Use brcm2835-sdhci for Rasperry PI.
+
+Use sdhci-iproc-cygnus for Broadcom SDHCI Controllers
+restricted to 32bit host accesses to SDHCI registers.
+
+Use sdhci-iproc for Broadcom SDHCI Controllers that allow standard
+8, 16, 32-bit host access to SDHCI register.
 
 - clocks : The clock feeding the SDHCI controller.