target/riscv: Add Zihintntl extension ISA string to DTS

target/riscv: Add Zihintntl extension ISA string to DTS

RVA23 Profiles states:
The RVA23 profiles are intended to be used for 64-bit application
processors that will run rich OS stacks from standard binary OS
distributions and with a substantial number of third-party binary user
applications that will be supported over a considerable length of time
in the field.

The chapter 4 of the unprivileged spec introduces the Zihintntl extension
and Zihintntl is a mandatory extension presented in RVA23 Profiles, whose
purpose is to enable application and operating system portability across
different implementations. Thus the DTS should contain the Zihintntl ISA
string in order to pass to software.

The unprivileged spec states:
Like any HINTs, these instructions may be freely ignored. Hence, although
they are described in terms of cache-based memory hierarchies, they do not
mandate the provision of caches.

These instructions are encoded with non-used opcode, e.g. ADD x0, x0, x2,
which QEMU already supports, and QEMU does not emulate cache. Therefore
these instructions can be considered as a no-op, and we only need to add
a new property for the Zihintntl extension.

Reviewed-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Jason Chien <jason.chien@sifive.com>
Message-ID: <20230726074049.19505-2-jason.chien@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>