Calculate required efiboot.img size instead of hardcoding it

Use du to count the file size of the kernel(s), initramfs images and boot loader (and its configuration).
This allows to compress initramfs with something other than xz, or have more than one kernel installed.

Fixes #62 .

archiso/mkarchiso

@@ -540,12 +540,21 @@ _make_boot_on_fat() {
 
 # Prepare efiboot.img::/EFI for EFI boot mode
 _make_boot_uefi-x64.systemd-boot.esp() {
+    local efiboot_imgsize="0"
     _msg_info "Setting up systemd-boot for UEFI booting..."
     install -d -m 0755 -- "${isofs_dir}/EFI/archiso"
 
+    efiboot_imgsize="$(( (( (( $(du --apparent-size -bc \
+        "${airootfs_dir}/usr/lib/systemd/boot/efi/systemd-bootx64.efi" \
+        "${airootfs_dir}/usr/share/edk2-shell/x64/Shell_Full.efi" \
+        "${profile}/efiboot/" \
+        "${airootfs_dir}/boot/vmlinuz-"* \
+        "${airootfs_dir}/boot/initramfs-"*".img" \
+        "${airootfs_dir}/boot/"{intel-uc.img,intel-ucode.img,amd-uc.img,amd-ucode.img,early_ucode.cpio,microcode.cpio} \
+        2>/dev/null | awk 'END {print $1}') / 1048576 )) +1 )) * 1024 ))"
     # The FAT image must be created with mkfs.fat not mformat, as some systems have issues with mformat made images:
     # https://lists.gnu.org/archive/html/grub-devel/2019-04/msg00099.html
-    mkfs.fat -C -n ARCHISO_EFI "${isofs_dir}/EFI/archiso/efiboot.img" 65536
+    mkfs.fat -C -n ARCHISO_EFI "${isofs_dir}/EFI/archiso/efiboot.img" "$efiboot_imgsize"
 
     mmd -i "${isofs_dir}/EFI/archiso/efiboot.img" ::/EFI ::/EFI/BOOT
     mcopy -i "${isofs_dir}/EFI/archiso/efiboot.img" \