icp: fix all !ENDBR objtool warnings in x86 Asm code

Currently, only Blake3 x86 Asm code has signs of being ENDBR-aware.
At least, under certain conditions it includes some header file and
uses some custom macro from there.
Linux has its own NOENDBR since several releases ago. It's defined
in the same <asm/linkage.h>, so currently <sys/asm_linkage.h>
already is provided with it.

Let's unify those two into one %ENDBR macro. At first, check if it's
present already. If so -- use Linux kernel version. Otherwise, try
to go that second way and use %_CET_ENDBR from <cet.h> if available.
If no, fall back to just empty definition.
This fixes a couple more 'relocations to !ENDBR' across the module.
And now that we always have the latest/actual ENDBR definition, use
it at the entrance of the few corresponding functions that objtool
still complains about. This matches the way how it's used in the
upstream x86 core Asm code.

Reviewed-by: Attila Fülöp <attila@fueloep.org>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Closes #14035

module/icp/asm-x86_64/modes/aesni-gcm-x86_64.S

@@ -59,6 +59,7 @@
 .align	32
 _aesni_ctr32_ghash_6x:
 .cfi_startproc
+	ENDBR
 	vmovdqu	32(%r11),%xmm2
 	subq	$6,%rdx
 	vpxor	%xmm4,%xmm4,%xmm4
@@ -375,6 +376,7 @@ _aesni_ctr32_ghash_6x:
 .align	32
 _aesni_ctr32_ghash_no_movbe_6x:
 .cfi_startproc
+	ENDBR
 	vmovdqu	32(%r11),%xmm2
 	subq	$6,%rdx
 	vpxor	%xmm4,%xmm4,%xmm4
@@ -703,6 +705,7 @@ _aesni_ctr32_ghash_no_movbe_6x:
 .align	32
 aesni_gcm_decrypt:
 .cfi_startproc
+	ENDBR
 	xorq	%r10,%r10
 	cmpq	$0x60,%rdx
 	jb	.Lgcm_dec_abort
@@ -820,6 +823,7 @@ aesni_gcm_decrypt:
 .align	32
 _aesni_ctr32_6x:
 .cfi_startproc
+	ENDBR
 	vmovdqu	0-128(%rcx),%xmm4
 	vmovdqu	32(%r11),%xmm2
 	leaq	-2(%rbp),%r13	// ICP uses 10,12,14 not 9,11,13 for rounds.
@@ -914,6 +918,7 @@ _aesni_ctr32_6x:
 .align	32
 aesni_gcm_encrypt:
 .cfi_startproc
+	ENDBR
 	xorq	%r10,%r10
 	cmpq	$288,%rdx
 	jb	.Lgcm_enc_abort