Recognize symbols with type SECTION

Sections must also be symbols so relocations referring to the addrs of those sections (as symbols) work.
See the following code:

```
0000000000000000 <init_module>:
   0:   55                      push   %rbp
   1:   48 c7 c7 00 00 00 00    mov    $0x0,%rdi
                        4: R_X86_64_32S .rodata.str1.1
   8:   31 c0                   xor    %eax,%eax
   a:   48 89 e5                mov    %rsp,%rbp
   d:   e8 00 00 00 00          callq  12 <init_module+0x12>
                        e: R_X86_64_PC32        printk-0x4
  12:   31 c0                   xor    %eax,%eax
  14:   5d                      pop    %rbp
  15:   c3                      retq  
```
First relocation is to a section .rodata.str1.1, second one is to printk.
r2 could only detect the symbol for the second one, but now also the first one:

```
   ;      [1] va=0x00000064 pa=0x00000064 sz=22 vsz=22 rwx=-r-x .init.text
╒ (fcn) sym.imp.printk 22
│          ;-- section..init.text:
│          0x00000064    55           push rbp
│          0x00000065    48c7c700000. mov rdi, 0x0  ;  RELOC 32 .rodata.str1.1
│          0x0000006c    31c0         xor eax, eax
│          0x0000006e    4889e5       mov rbp, rsp
│          0x00000071    e800000000   call 0x76 ; (sym.imp.printk)
│             sym.imp.printk(unk) ; sym.__UNIQUE_ID_author1+1  ;  RELOC 32 printk
│          ; CALL XREF from 0x00000071 (unk)
│          0x00000076    31c0         xor eax, eax
│          0x00000078    5d           pop rbp
╘          0x00000079    c3           ret
```