Remove memory allocation for ELF sections

[LambertWSJ]

Since the section headers of ELF are continuous, all headers can be accessed by getting the starting address, so there is no need to allocate memory for this.

[jserv]

Eliminate the warnings reported by Codacy/Cppcheck.

[jserv]

Eliminate the warnings reported by Codacy/Cppcheck.

Reported by Cppcheck:

tools/rv_histogram.c:192:31: style: Parameter 'ir' can be declared as pointer to const [constParameterPointer]
void reg_hist_incr(rv_insn_t *ir)
                              ^
tools/rv_histogram.c:217:32: style: Parameter 'ir' can be declared as pointer to const. However it seems that 'insn_hist_incr' is a callback function, if 'ir' is declared with const you might also need to cast function pointer(s). [constParameterCallback]
void insn_hist_incr(rv_insn_t *ir)
                               ^
tools/rv_histogram.c:235:46: note: You might need to cast the function pointer here
    hist_record = show_reg ? reg_hist_incr : insn_hist_incr;
                                             ^
tools/rv_histogram.c:217:32: note: Parameter 'ir' can be declared as pointer to const
void insn_hist_incr(rv_insn_t *ir)
                               ^
tools/rv_histogram.c:253:28: style: Variable 'shdr' can be declared as pointer to const [constVariablePointer]
        struct Elf32_Shdr *shdr = (struct Elf32_Shdr *) shdrs + i;
                           ^
tools/rv_histogram.c:260:20: style: Variable 'exec_end_addr' can be declared as pointer to const [constVariablePointer]
        uintptr_t *exec_end_addr =
                   ^

@LambertWSJ, you may submit pull requests to eliminate the warnings reported by Cppcheck later.