Fix GDB sparc build

Fix GDB sparc build

Cross-compiling for sparc64 bumped into a few issues, fixed by this
patch.

1. Include target.h in sparc-nat.h fixes:

/home/emaisin/src/binutils-gdb/gdb/sparc-nat.h:45:8: error: ‘target_xfer_status’ does not name a type
 extern target_xfer_status sparc_xfer_wcookie (enum target_object object,

2. Remove extra semi-colon at sparc64-linux-nat.c:40 fixes:

/home/emaisin/src/binutils-gdb/gdb/sparc64-linux-nat.c:41:3: error: expected unqualified-id before ‘{’ token
   { sparc_store_inferior_registers (this, regcache, regnum); }

3. Remove "this" argument fixes:

/home/emaisin/src/binutils-gdb/gdb/sparc64-linux-nat.c: In member function ‘virtual void sparc64_linux_nat_target::fetch_registers(regcache*, int)’:
/home/emaisin/src/binutils-gdb/gdb/sparc64-linux-nat.c:38:59: error: cannot convert ‘sparc64_linux_nat_target*’ to ‘regcache*’ for argument ‘1’ to ‘void sparc_fetch_inferior_registers(regcache*, int)’
   { sparc_fetch_inferior_registers (this, regcache, regnum); }
                                                           ^
/home/emaisin/src/binutils-gdb/gdb/sparc64-linux-nat.c: In member function ‘virtual void sparc64_linux_nat_target::store_registers(regcache*, int)’:
/home/emaisin/src/binutils-gdb/gdb/sparc64-linux-nat.c:41:59: error: cannot convert ‘sparc64_linux_nat_target*’ to ‘regcache*’ for argument ‘1’ to ‘void sparc_store_inferior_registers(regcache*, int)’
   { sparc_store_inferior_registers (this, regcache, regnum); }
                                                           ^
4. Use sparc64_forget_process instead of sparc_forget_process fixes:

/home/emaisin/src/binutils-gdb/gdb/sparc64-linux-nat.c: In member function ‘virtual void sparc64_linux_nat_target::low_forget_process(pid_t)’:
/home/emaisin/src/binutils-gdb/gdb/sparc64-linux-nat.c:47:30: error: ‘sparc_forget_process’ was not declared in this scope
   { sparc_forget_process (pid); }
                              ^

gdb/ChangeLog:

	* sparc-nat.h: Include target.h.
	* sparc64-linux-nat.c (class sparc64_linux_nat_target)
	<fetch_registers>: Remove this argument in function call.
	<store_registers>: Remove this argument in function call, remove
	extra semicolon.
	<low_forget_process>: Call sparc64_forget_process instead of
	sparc_forget_process.