bsd-user: Implement RISC-V TLS register setup

bsd-user: Implement RISC-V TLS register setup

Included the prototype for the 'target_cpu_set_tls' function in the
'target_arch.h' header file. This function is responsible for setting
the Thread Local Storage (TLS) register for RISC-V architecture.

Signed-off-by: Mark Corbin <mark@dibsco.co.uk>
Signed-off-by: Ajeet Singh <itachis@FreeBSD.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20240916155119.14610-5-itachis@FreeBSD.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>