tools/nolibc: MIPS: drop $gp setup

The setup of the global pointer "$gp" register was necessary when the C
entrypoint was called through "jal <symbol>".
However since commit 0daf8c8 ("tools/nolibc: mips: load current function to $t9")
"jalr" is used instead which does not require "$gp".

Remove the unnecessary $gp setup, simplifying the code and opening the
road for some other cleanups.

Suggested-by: Maciej W. Rozycki <macro@orcam.me.uk>
Link: https://lore.kernel.org/lkml/alpine.DEB.2.21.2502172208570.65342@angie.orcam.me.uk/
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Tested-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Link: https://lore.kernel.org/r/20250623-nolibc-mips-n32-v3-1-6ae2d89f4259@weissschuh.net

Author: t-8ch

tools/include/nolibc/arch-mips.h

@@ -185,13 +185,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector __
 	__asm__ volatile (
 		".set push\n"
 		".set noreorder\n"
-		"bal 1f\n"               /* prime $ra for .cpload                            */
-		"nop\n"
-		"1:\n"
-		".cpload $ra\n"
 		"move  $a0, $sp\n"       /* save stack pointer to $a0, as arg1 of _start_c */
-		"addiu $sp, $sp, -4\n"   /* space for .cprestore to store $gp              */
-		".cprestore 0\n"
 		"li    $t0, -8\n"
 		"and   $sp, $sp, $t0\n"  /* $sp must be 8-byte aligned                     */
 		"addiu $sp, $sp, -16\n"  /* the callee expects to save a0..a3 there        */