bcm4908: add testing support for kernel 5.10

CONFIG_COMPAT_32BIT_TIME is a new symbol and has to be set to avoid:
Provide system calls for 32-bit time_t (COMPAT_32BIT_TIME) [N/y/?] (NEW)

CONFIG_RELOCATABLE needs to be enabled to make kernel start booting.
That raises a question: do we really need CONFIG_EXPERT=y ?

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

target/linux/bcm4908/Makefile

@@ -10,7 +10,7 @@ CPU_TYPE:=cortex-a53
 SUBTARGETS:=generic
 
 KERNEL_PATCHVER:=5.4
-KERNEL_TESTING_PATCHVER:=5.4
+KERNEL_TESTING_PATCHVER:=5.10
 
 define Target/Description
 	Build firmware images for Broadcom BCM4908 SoC family routers.

target/linux/bcm4908/config-5.10

@@ -50,6 +50,7 @@ CONFIG_CLONE_BACKWARDS=y
 CONFIG_CMDLINE="earlycon=bcm63xx_uart,0xff800640 console=ttyS0,115200"
 CONFIG_CMDLINE_FORCE=y
 CONFIG_COMMON_CLK=y
+# CONFIG_COMPAT_32BIT_TIME is not set
 CONFIG_CPU_RMAP=y
 CONFIG_CRC16=y
 CONFIG_CRYPTO_ACOMP2=y
@@ -183,6 +184,7 @@ CONFIG_RATIONAL=y
 CONFIG_REFCOUNT_FULL=y
 CONFIG_REGMAP=y
 CONFIG_REGMAP_MMIO=y
+CONFIG_RELOCATABLE=y
 CONFIG_RFS_ACCEL=y
 CONFIG_RODATA_FULL_DEFAULT_ENABLED=y
 CONFIG_RPS=y