luckfox-rk3308b-nova: bump U-Boot to v2026.07-rc4

The board was merged on U-Boot v2025.04. Move it to v2026.07-rc4.

Two of the six board patches - the dw_mmc fixes dwmci_control_clken()
CDONE acknowledge and dwmci_setup_bus() same-frequency skip - have since
landed upstream, so drop them. The remaining four (board defconfig/DTS,
the evb_rk3308 download-key saradc device-name fix, the 1-bit DT
bus-width honoring, and RockUSB-on-download-key) apply cleanly to
v2026.07-rc4.

Tested on hardware: SPL -> U-Boot v2026.07-rc4 boots and brings up both
the current (6.18) and edge (7.1) kernels; the SARADC recovery key and
RockUSB download mode both work.

Signed-off-by: crackerjacques <jack@supremeoverlordjabs.co>

Author: crackerjacques

config/boards/luckfox-rk3308b-nova.csc

@@ -17,8 +17,8 @@ SERIALCON="ttyS4"
 HAS_VIDEO_OUTPUT="no"
 MODULES_BLACKLIST="rockchipdrm analogix_dp dw_mipi_dsi dw_hdmi gpu_sched lima hantro_vpu panfrost"
 
-BOOTBRANCH_BOARD="tag:v2025.04"
-BOOTPATCHDIR="v2025.04"
+BOOTBRANCH_BOARD="tag:v2026.07-rc4"
+BOOTPATCHDIR="v2026.07"
 BOOT_SCENARIO="binman"
 BOOTFS_TYPE="ext4"
 IMAGE_PARTITION_TABLE="gpt"