mmc: msm: fix compile error on MSM7x30

MSM7x30 isn't supported in this driver yet. If ones tried to compile it in
with MSM7x30 configure you get,

linux-2.6/drivers/mmc/host/msm_sdcc.c: In function 'msmsdcc_fifo_addr':
linux-2.6/drivers/mmc/host/msm_sdcc.c:165: error: 'MSM_SDC1_PHYS' undeclared (first use in this function)
linux-2.6/drivers/mmc/host/msm_sdcc.c:165: error: (Each undeclared identifier is reported only once
linux-2.6/drivers/mmc/host/msm_sdcc.c:165: error: for each function it appears in.)
linux-2.6/drivers/mmc/host/msm_sdcc.c:167: error: 'MSM_SDC2_PHYS' undeclared (first use in this function)
linux-2.6/drivers/mmc/host/msm_sdcc.c:169: error: 'MSM_SDC3_PHYS' undeclared (first use in this function)
linux-2.6/drivers/mmc/host/msm_sdcc.c:171: error: 'MSM_SDC4_PHYS' undeclared (first use in this function)

So we add a Kconfig check to prevent this.

Signed-off-by: Daniel Walker <dwalker@codeaurora.org>