target/xtensa: gdbstub fix register counting

target/xtensa: gdbstub fix register counting

In order to communicate correctly with gdb xtensa gdbstub must provide
expected number of registers in 'g' packet response. xtensa-elf-gdb
expects both nonprivileged and privileged registers. xtensa-linux-gdb
only expects nonprivileged registers. gdb only counts one contiguous
stretch of registers, do the same for the core registers in the
xtensa_count_regs.

With this change qemu-system-xtensa is able to communicate with all
xtensa-elf-gdb versions (versions prior to 8.2 require overlay fixup),
and qemu-xtensa is able to communicate with all xtensa-linux-gdb
versions, except 8.2.

Signed-off-by: Max Filippov <[email protected]>