This commit adds support for catching syscalls on riscv

This commit adds support for catching syscalls on riscv

It affects following files:
- gdb/riscv-linux-tdep.c: a function to get syscall number.
- gdbserver/linux-riscv-low.cc: syscall trapinfo function to enable
catching syscalls on remote targets.
- gdb/syscalls/riscv-linux.xml.in: a file with syscalls, generated from
linux kernel sources using gdb/syscalls/update-linux-from-src.sh script.
- gdb/syscalls/riscv-linux.xml: a file with syscalls, patched with group
names gdb/syscalls/apply-defaults.xsl using xsltproc tool.
- gdb/syscalls/update-linux.sh: set startyear to 2025 on riscv.
- gdb/syscalls/update-linux-from-src.sh: riscv syscall table must be
generated from kernel headers.
- gdb/NEWS: catch-syscall feature is now available on riscv.
- gdb/data-directory/Makefile.in: adding file with syscalls to Makefile.

Approved-By: Tom Tromey <tom@tromey.com>