dt-bindings: riscv: fix underscore requirement for multi-letter extensions

The RISC-V ISA Manual allows the first multi-letter extension to avoid
a leading underscore. Underscores are only required between multi-letter
extensions.

The dt-binding does not validate that a multi-letter extension is
canonically ordered, as that'd need an even worse regex than is here,
but it should not fail validation for valid ISA strings.

Allow the first multi-letter extension to appear immediately after
the single-letter extensions.

Link: https://github.com/riscv/riscv-isa-manual/releases/tag/riscv-unpriv-pdf-from-asciidoc-15112022 # Chapter 29.5
Fixes: 299824e68bd0 ("dt-bindings: riscv: add new riscv,isa strings for emulators")
Acked-by: Guo Ren <[email protected]>
Signed-off-by: Conor Dooley <[email protected]>
Acked-by: Rob Herring <[email protected]>
Reviewed-by: Palmer Dabbelt <[email protected]>
Acked-by: Palmer Dabbelt <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

0 files changed, 0 insertions, 0 deletions