msm_serial_hs: Dynamic allocation of port structures

This patch allocates the msm_hs_port structures
dynamically during probe and cleans up during exit.
The msm_hs_get_uart_port function now looks up the
uart_state data structure to find the right uart_port.

Change-Id: I3876959eb41173d2115d2c1acfc612b75ca2e46a
Signed-off-by: Naveen Kaje <nkaje@codeaurora.org>