tf-a-stm32mp: Add bbappend for trusted firmware. Patch dts name.

New version of the trusted firmware uses dts names that are
assembled in runtime by the script in bb recipe.
The base name is derived from STM32MP_DEVICETREE variable
which for Avenger contains "av96" rather than "avenger96"
string. This causes mismatch either in meta-st-stm32mp layer or
in meta-av96 if changed in the latter one.

Introduce workaround that will allow to avoid modifying ST
layer, minimize diff in meta-av96 and satisfy convoluted build
requirements for names, etc.

Signed-off-by: Zbigniew Bodek <zbigniew.bodek@huawei.com>
13 jobs for !10 with zb/linux_5.10 in 44 minutes and 33 seconds (queued for 4 seconds)
detached
Status Job ID Name Coverage
  Compliance
passed #17785
dco

00:00:12

 
  Build
passed #17797
large-disk
freertos-armv5

00:04:16

passed #17788
large-disk
linux-qemu-arm

00:14:36

passed #17789
large-disk
linux-qemu-arm64

00:15:52

passed #17786
large-disk
linux-qemu-x86

00:16:38

passed #17787
large-disk
linux-qemu-x86_64

00:16:29

passed #17791
large-disk
linux-seco-imx8mm-c61

00:17:36

passed #17790
large-disk
linux-seco-intel-b68

00:18:03

passed #17792
large-disk
linux-stm32mp1-av96

00:27:42

passed #17796
large-disk
zephyr-96b-avenger

00:03:59

passed #17795
large-disk
zephyr-96b-nitrogen

00:02:54

passed #17794
large-disk
zephyr-qemu-cortex-m3

00:03:04

passed #17793
large-disk
zephyr-qemu-x86

00:03:31