Where is boot partition?

[dasssnj]

Hi, i'm searching for the boot partition on Xperia mini pro and i can't find it. On other devices it's usually '/dev/block/mtdblockx' but on this device it's not.
There is no /boot directory at all. I'm wondering why we should use fastboot to flash boot.img instead of flashing it with the device itself ? (like some other devices)

I'm using Legacy xperia cm 13.0 and i this is 'fstab.semc' file in the root directory:

# Android fstab file.
#<src>                                        <mnt_point>    <type>    <mnt_flags>               <fs_mgr_flags>
# The filesystem that contains the filesystem checker binary (typically /system) cannot
# specify MF_CHECK, and must come before any filesystems that do specify MF_CHECK

/dev/null                             /boot          mtd       defaults                                                                              defaults
/dev/null                             /recovery      mtd       defaults                                                                              defaults
/dev/block/mtd/by-name/system         /system        yaffs2    ro                                                                                    wait
/dev/block/mtd/by-name/cache          /cache         yaffs2    rw,noatime,nosuid,nodev                                                               wait
/dev/block/mmcblk0p1                  /data          f2fs      rw,discard,nosuid,nodev,noatime,nodiratime,inline_xattr                               wait,check,formattable
/dev/block/mmcblk0p1                  /data          ext4      noatime,nosuid,nodev,data=ordered,noauto_da_alloc,journal_async_commit,errors=panic   wait,check

# Vold managed devices
/devices/platform/msm_hsusb_host.0*   auto           auto      defaults                                                                              voldmanaged=usb:auto

# zRAM
/dev/block/zram0                      none           swap      defaults                                                                              zramsize=134217728

How is this possible? Why it's pointing to /dev/null ?
I'm just wondering which partition fastboot uses to flash the kernel img ? And is this possible for us to find the partition and flash the kernel with phone using dd ?
Can anyone explain it to me?
Thank you.