Merge remote-tracking branch 'remotes/alistair/tags/pull-riscv-to-apply-20210608-1' into staging

Second RISC-V PR for QEMU 6.1

 - Update the PLIC and CLINT DT bindings
 - Improve documentation for RISC-V machines
 - Support direct kernel boot for microchip_pfsoc
 - Fix WFI exception behaviour
 - Improve CSR printing
 - Initial support for the experimental Bit Manip extension

# gpg: Signature made Tue 08 Jun 2021 01:28:27 BST
# gpg:                using RSA key F6C4AC46D4934868D3B8CE8F21E10D29DF977054
# gpg: Good signature from "Alistair Francis <alistair@alistair23.me>" [full]
# Primary key fingerprint: F6C4 AC46 D493 4868 D3B8  CE8F 21E1 0D29 DF97 7054

* remotes/alistair/tags/pull-riscv-to-apply-20210608-1: (32 commits)
  target/riscv: rvb: add b-ext version cpu option
  target/riscv: rvb: support and turn on B-extension from command line
  target/riscv: rvb: add/shift with prefix zero-extend
  target/riscv: rvb: address calculation
  target/riscv: rvb: generalized or-combine
  target/riscv: rvb: generalized reverse
  target/riscv: rvb: rotate (left/right)
  target/riscv: rvb: shift ones
  target/riscv: rvb: single-bit instructions
  target/riscv: add gen_shifti() and gen_shiftiw() helper functions
  target/riscv: rvb: sign-extend instructions
  target/riscv: rvb: min/max instructions
  target/riscv: rvb: pack two words into one register
  target/riscv: rvb: logic-with-negate
  target/riscv: rvb: count bits set
  target/riscv: rvb: count leading/trailing zeros
  target/riscv: reformat @sh format encoding for B-extension
  target/riscv: Pass the same value to oprsz and maxsz.
  target/riscv/pmp: Add assert for ePMP operations
  target/riscv: Dump CSR mscratch/sscratch/satp
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>