msm: scm-boot: Clarify types for scm_set_boot_addr()

The boot address is a physical address (even if the secure
monitor only considers it to be 32 bits). Move to using
phys_addr_t to clarify this is a physical address and to ease
any support of LPAE in the future. Also make the flags unsigned
so that we can use the highest bit if necessary.

Change-Id: I1aa5ca9cb75ea94b4df72c5a536cf42f73ff8051
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>