brcm2708: bcm2708: fix build

buildbot fails to build without regmap, which I couldn't reproduce locally.
Hopefully this fixes it.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

target/linux/brcm2708/bcm2708/config-4.9

@@ -233,12 +233,15 @@ CONFIG_LOGO=y
 CONFIG_LOGO_LINUX_CLUT224=y
 # CONFIG_LOGO_LINUX_MONO is not set
 # CONFIG_LOGO_LINUX_VGA16 is not set
+CONFIG_LZO_COMPRESS=y
+CONFIG_LZO_DECOMPRESS=y
 CONFIG_MAC_PARTITION=y
 CONFIG_MAGIC_SYSRQ=y
 CONFIG_MAILBOX=y
 # CONFIG_MAILBOX_TEST is not set
 CONFIG_MAX_RAW_DEVS=256
 CONFIG_MEMORY_ISOLATION=y
+CONFIG_MFD_SYSCON=y
 CONFIG_MIGHT_HAVE_CACHE_L2X0=y
 CONFIG_MIGHT_HAVE_PCI=y
 CONFIG_MIGRATION=y
@@ -304,6 +307,8 @@ CONFIG_RASPBERRYPI_POWER=y
 CONFIG_RATIONAL=y
 CONFIG_RAW_DRIVER=y
 # CONFIG_RCU_STALL_COMMON is not set
+CONFIG_REGMAP=y
+CONFIG_REGMAP_MMIO=y
 CONFIG_REGULATOR=y
 CONFIG_REGULATOR_FIXED_VOLTAGE=y
 CONFIG_RWSEM_XCHGADD_ALGORITHM=y