ipq40xx: add CONFIG_NVMEM_BLOCK

NVMEM on MMC was added in dts but the corresponding option was not added
to the config.

Fixes: ee5999c ("treewide: linksys: use nvmem MAC for hw_mac_addr")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: openwrt#22539
Signed-off-by: Robert Marko <robert.marko@sartura.hr>
(cherry picked from commit 8f33ecf)

Author: neheb

target/linux/ipq40xx/config-6.12

@@ -330,6 +330,7 @@ CONFIG_NO_HZ_COMMON=y
 CONFIG_NO_HZ_IDLE=y
 CONFIG_NR_CPUS=4
 CONFIG_NVMEM=y
+CONFIG_NVMEM_BLOCK=y
 CONFIG_NVMEM_LAYOUTS=y
 CONFIG_NVMEM_LAYOUT_ASCII_ENV=y
 CONFIG_NVMEM_LAYOUT_U_BOOT_ENV=y