MIPS: module: optimize module relocations processing

For now, module relocation functions are implemented as an array
of handlers of type reloc_handler_t.

Convert that array into a single switch-case function to:
 - remove unused arguments;
 - change the return type of simple handlers to void;
 - remove the array and don't use any data at all;
 - avoid using indirect calls;
 - allow the compiler to inline and greatly optimize
   the relocation function[s].

The result on MIPS32 R2 with GCC 10.2 -O2 is:

scripts/bloat-o-meter -c arch/mips/kernel/__module.o arch/mips/kernel/module.o
add/remove: 1/11 grow/shrink: 1/0 up/down: 876/-1436 (-560)
Function                                     old     new   delta
apply_relocate                               456    1148    +692
apply_r_mips_pc                                -     184    +184
apply_r_mips_none                              8       -      -8
apply_r_mips_32                               16       -     -16
apply_r_mips_64                               76       -     -76
apply_r_mips_highest                          88       -     -88
apply_r_mips_higher                          108       -    -108
apply_r_mips_26                              132       -    -132
apply_r_mips_pc26                            160       -    -160
apply_r_mips_pc21                            160       -    -160
apply_r_mips_pc16                            160       -    -160
apply_r_mips_hi16                            172       -    -172
apply_r_mips_lo16                            356       -    -356
Total: Before=2608, After=2048, chg -21.47%
add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0 (0)
Data                                         old     new   delta
Total: Before=12, After=12, chg +0.00%
add/remove: 0/1 grow/shrink: 0/0 up/down: 0/-248 (-248)
RO Data                                      old     new   delta
reloc_handlers                               248       -    -248
Total: Before=248, After=0, chg -100.00%

All functions were collapsed into a single one that is called
directly by $(srctree)/kernel/module.c.

Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>