unix: add consts and structs for <mtd/mtd-user.h>

It would be convenient to have MTD user space consts and structs
in the package.

Checked that the regexes in unix/mkerrors.sh are not too general,
and that all the defined constants in <mtd/mtd-user.h> are included
in the generated code.

Checked that all structs and enums added in unix/linux/types.go
are complete.

Fixes golang/go#46063
Change-Id: I190ac290f3f32a4f817cc7506df0dddb24d881b8
Reviewed-on: https://go-review.googlesource.com/c/sys/+/318211
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>

unix/mkerrors.sh

@@ -258,6 +258,7 @@ struct ltchars {
 #include <linux/watchdog.h>
 
 #include <mtd/ubi-user.h>
+#include <mtd/mtd-user.h>
 #include <net/route.h>
 
 #if defined(__sparc__)
@@ -593,6 +594,9 @@ ccflags="$@"
 		$2 == "HID_MAX_DESCRIPTOR_SIZE" ||
 		$2 ~ /^_?HIDIOC/ ||
 		$2 ~ /^BUS_(USB|HIL|BLUETOOTH|VIRTUAL)$/ ||
+		$2 ~ /^MTD_/ ||
+		$2 ~ /^OTP/ ||
+		$2 ~ /^MEM/ ||
 		$2 ~ /^BLK[A-Z]*(GET$|SET$|BUF$|PART$|SIZE)/ {printf("\t%s = C.%s\n", $2, $2)}
 		$2 ~ /^__WCOREFLAG$/ {next}
 		$2 ~ /^__W[A-Z0-9]+$/ {printf("\t%s = C.%s\n", substr($2,3), $2)}