sc7280: Provide initial SoC support

BUG=b:182963902
TEST=Validated on qualcomm sc7280 developement board

Change-Id: I1fc841b3113f2bf79b8376cd1ccdb671c53c2084
Signed-off-by: T Michael Turney <mturney@codeaurora.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45205
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Shelley Chen <shchen@google.com>

Documentation/soc/qualcomm/index.md

@@ -5,3 +5,4 @@ This section contains documentation about coreboot on specific Qualcomm SOCs.
 ## Platforms
 
 - [SC7180 series](sc7180/index.md)
+- [SC7280 series](sc7280/index.md)

Documentation/soc/qualcomm/sc7280/index.md

@@ -0,0 +1,17 @@
+# Qualcomm SC7280 documentation
+
+## SOC code
+
+The SOC folder contains functions for:
+* MMU
+* CLOCK
+* GPIO
+* QUPv3 FW (provides a bridge to serial interfaces)
+* UART
+* SPI-NOR
+* AOP FW
+* USB
+
+## Notes about the hardware
+
+The timer is used from the ARMv8 architecture specific code.