u-boot-updatehub-script: Allow addition of extra fragments
u-boot-updatehub-script: Allow addition of extra fragments

Allow inclusion of extra boot script fragment, using
UPDATEHUB_BOOTSCRIPT_BEFORE_BOOTCMD, to be run before running the
UPDATEHUB_BOOTSCRIPT_BOOTCMD fragment, for example using `fdt` command
to enable/disable device tree handles.

Example:

,----[ UPDATEHUB_BOOTSCRIPT_BEFORE_BOOTCMD example ]
| fdt addr \${fdt_addr_r}; \
| fdt resize; \
| if itest.s "x" == "x\${lvds_size}"; then \
|    lvds_size="10";
| fi \
| \
| if itest.s "x10" == "x\${lvds_size}"; then \
|    fdt set /panel compatible "aison,z101wx02jct736"; \
| elif itest.s "x8" == "x\${lvds_size}"; then \
|    fdt set /panel compatible "aison,z080xg03jct3"; \
| else \
|    echo "ERROR: Unknown 'lvds_size'. Valid ones are '10' and '8'."; \
| fi
`----

Signed-off-by: Otavio Salvador <1d31b11c1b92bf5d043d36edfe7174db39a6b891@ossystems.com.br>

UpdateHub/meta-updatehub,UpdateHub/meta-updatehub,UpdateHub/meta-updatehub