package/gnu-efi: fix efilink for systemd-boot

package/gnu-efi: fix efilink for systemd-boot

This fixes a compilation error when building with systemd with systemd-boot
enabled.

Fixes:
>>> systemd 241 Building
PATH="/home/buildroot/buildroot/output/host/bin:/home/buildroot/buildroot/output/host/sbin:/home/buildroot/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin" LC_ALL=en_US.UTF-8 PYTHONNOUSERSITE=y /home/buildroot/buildroot/output/host/bin/ninja  -j33  -C /home/buildroot/buildroot/output/build/systemd-241//build
ninja: Entering directory `/home/buildroot/buildroot/output/build/systemd-241//build'
[458/805] Generating disk.c.o with a custom command.
FAILED: src/boot/efi/disk.c.o
/home/buildroot/buildroot/output/host/bin/i686-buildroot-linux-gnu-gcc -c ../src/boot/efi/disk.c -o src/boot/efi/disk.c.o -Wall -Wextra -std=gnu90 -nostdinc -ggdb -O0 -fpic -fshort-wchar -ffreestanding -fno-strict-aliasing -fno-stack-protector -Wsign-compare -Wno-missing-field-initializers -isystem /home/buildroot/buildroot/output/host/i686-buildroot-linux-gnu/sysroot/usr/include/efi -isystem /home/buildroot/buildroot/output/host/i686-buildroot-linux-gnu/sysroot/usr/include/efi/ia32 -include src/boot/efi/efi_config.h -include version.h
In file included from /home/buildroot/buildroot/output/host/i686-buildroot-linux-gnu/sysroot/usr/include/efi/efilib.h:25,
                 from ../src/boot/efi/disk.c:4:
/home/buildroot/buildroot/output/host/i686-buildroot-linux-gnu/sysroot/usr/include/efi/efilink.h:5:10: fatal error: stdint.h: No such file or directory
 #include <stdint.h>
          ^~~~~~~~~~
compilation terminated.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>