RISC-V: add U-type imm parsing to insn.h header

Similar to other existing types, allow extracting the immediate
for a U-type instruction.

U-type immediates are special in that regard, that the value
in the instruction in bits [31:12] already represents the same
bits of the immediate, so no shifting is required.

U-type immediates are for example used in the auipc instruction,
so these constants make it easier to parse such instructions.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Link: https://lore.kernel.org/r/20221223221332.4127602-10-heiko@sntech.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/insn.h

@@ -34,6 +34,15 @@
 #define RV_J_IMM_11_MASK	GENMASK(0, 0)
 #define RV_J_IMM_19_12_MASK	GENMASK(7, 0)
 
+/*
+ * U-type IMMs contain the upper 20bits [31:20] of an immediate with
+ * the rest filled in by zeros, so no shifting required. Similarly,
+ * bit31 contains the signed state, so no sign extension necessary.
+ */
+#define RV_U_IMM_SIGN_OPOFF	31
+#define RV_U_IMM_31_12_OPOFF	0
+#define RV_U_IMM_31_12_MASK	GENMASK(31, 12)
+
 /* The bit field of immediate value in B-type instruction */
 #define RV_B_IMM_SIGN_OPOFF	31
 #define RV_B_IMM_10_5_OPOFF	25
@@ -235,6 +244,10 @@ static __always_inline bool riscv_insn_is_branch(u32 code)
 #define RV_X(X, s, mask)  (((X) >> (s)) & (mask))
 #define RVC_X(X, s, mask) RV_X(X, s, mask)
 
+#define RV_EXTRACT_UTYPE_IMM(x) \
+	({typeof(x) x_ = (x); \
+	(RV_X(x_, RV_U_IMM_31_12_OPOFF, RV_U_IMM_31_12_MASK)); })
+
 #define RV_EXTRACT_JTYPE_IMM(x) \
 	({typeof(x) x_ = (x); \
 	(RV_X(x_, RV_J_IMM_10_1_OPOFF, RV_J_IMM_10_1_MASK) << RV_J_IMM_10_1_OFF) | \